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^Heredity   of    Coat    Characters   in 
Guinea-Pigs  and  Rabbits, 


BY 


W.  E.  CASTLE 

Assistant  Professor  of  Zoology,  Harvard  University 
Associate,  Station  for  Experimental  Evolution 


Drf 


PUBLISHED  BY  THE  CARNEGIE  INSTITUTION  OF  WASHINGTON 
FEBRUARY,   1905 


CARNEGIE  INSTITUTION  OF  WASHINGTON,  PUBLICATION  No.  23. 


PAPERS  OF  STATION  FOR  EXPERIMENTAL  EVOLUTION  AT 
COLD  SPRING  HARBOR,  NEW  YORK.     No.  2. 


CONTRIBUTIONS   FROM  ZOOLOGICAL  LABORATORY   OF   MUSEUM   OF   COMPARA- 
TIVE ZOOLOGY  AT  HARVARD  COLLEGE.     E.  L.  MARK,  DIRECTOR.     No.  158. 


PRESS  OF  GIBSON  BROS., 
WASHINGTON,  D.  C. 


CONTENTS. 


Introduction, , 5 

Experiments  with  guinea-pigs,          . 6 

Heredity  of  coat  color,    .         .         .         . 6 

Coat  of  the  wild  cavy, 6 

Color  varieties  of  the  domesticated  cavy  or  guinea-pig,  ....       7 

Agouti,      .  ...         . 7 

Yellow, 7 

Chocolate, 7 

Black,        .....,_ 8 

Albino,      ..'.'. 8 

Spotted,    .         .         .         ..'.".• 12 

Brindled, 13 

Roan,  and  Silvered,          .         .         ...         .         .         .         .         -14 

Results  of  crossing  the  elementary  color  varieties,    .         .         .         .         .14 

Albinos  and  pigmented  animals,     .         .  •       .        ,        ',        .        .        .14 
Albinism  and  the  "Law  of  ancestral  heredjty,"      .»••:.        .        «        .     16 
Albinism  and  sexual  prepotency,        .         .         .         .         .        .        .        .     33 

Albinism  and  latent  pigment  characters,  .  .        .        ;        .     34 

Intercrossing  of  different  pigment  types,  .         .         .         .  .     a6 

The  agouti  type,       .         .         .         .         .....         .         .26 

Agouti  X  agouti, 26 

Agouti  x  black, .....         .26 

Agouti  X  red. .         .         ,      .   .         .28 

Agouti  x  albino, .        .         .         .28 

The  black  type, 31 

Black  x  red, 31 

Black  x  albino,    .         .         .         .  ...        .        .         -34 

The  red  type,    .         .         .         .        .         .         .         .        %       .  .36 

Red  x  albino, 37 

Black-eyed  white, -37 

Comparison  with  pink-eyed  mice,        .         .  ;         .         .         -47 

Heredity  of  rough  coat, 56 

Prepotency  and  dominance, .        .         .58 

Heredity  of  long  coat 64 

Correlation  among  coat  characters,       .  ......     67 

Experiments  with  rabbits, 70 

Cross  between  two  different  types  of  albinos,        ....         .•       .        .70 
Heredity  of  long  or  Angora  coat,  «,      •        •         •         •        •        •        -73 

Herediiy  of  lop-ears,       .         .         .         ,         *      .  • 74 

Summary,           .         .                                                                                 •         •         •     75 
Bibliography, 77 


HEREDITY  OF  COAT  CHARACTERS  IN 
GUINEA-PIGS  AND  RABBITS. 


BY  W.  E.  CASTLE. 


INTRODUCTION. 

The  experiments  to  be  described  in  this  paper  have  been  in  progress 
in  the  Zoological  Laboratory  of  Harvard  University  since  the  year  1900 . 
They  were  begun  for  the  study  of  conditions  governing  sex  in  the  higher 
animals,  but  have  yielded  results  bearing  on  certain  other  questions, 
which  alone  will  be  considered  in  this  paper. 

The  animals  used,  guinea-pigs  and  rabbits,  were  selected  because  of 
their  early  maturity  and  fecundity.  To  provide  them  with  food  and 
shelter  and  to  give  them  the  necessary  daily  care,  in  addition  to  keep- 
ing records  as  full  as  possible,  have  been  no  small  task.  In  this  con- 
nection I  am  indebted  for  invaluable  assistance  to  a  number  of  per- 
sons. First  of  all  to  Prof.  E.  L.  Mark,  director  of  the  zoological 
laboratory,  without  whose  encouragement  and  support  the  experi- 
ments could  never  have  been  undertaken,  and  who  has  more  than 
once  come  to  the  rescue  when  the  material  resources  at  my  command 
were  exhausted  and  further  progress  seemed  impossible.  The  director 
and  other  officers  of  the  Museum  of  Comparative  Zoology,  and  the 
President  of  the  University,  have  generously  provided  quarters  for  the 
animals  and  in  other  ways  have  aided  the  enterprise.  Finally,  when 
the  increasing  cost  became  a  burden  too  heavy  for  the  laboratory  to 
bear,  it  was  assumed  by  the  Carnegie  Institution  of  Washington  in  the 
form  of  a  grant  to  Professor  Mark  and  myself  for  experimental  studies 
in  heredity.  Under  the  auspices  of  the  Carnegie  Institution  the  work 
has  been  in  progress  since  January,  1904,  and  this  paper  is  presented 
as  a  first  detailed  report  upon  it. 

In  the  course  of  the  experiments  about  3,000  guinea-pigs  and  several 
hundred  rabbits  have  been  reared. 

For  valuable  guinea-pigs  and  excellent  practical  suggestions  I  am 
indebted  to  Miss  Jeannette  Soule,  secretary  of  the  National  Cavy  Club  ; 
for  an  interesting  stock  of  albino  rabbits  I  am  indebted  to  Prof.  R.  T. 

5 


6  COAT    CHARACTERS    IN    GUINEA-PIGS    AND    RABBITS. 

Jackson.  During  the  academic  year  1903-1904,  Mr.  R.  C.  Kibbey  has 
given  me  valuable  assistance  in  the  breeding  experiments,  and  Mr. 
A.  D.  Howard  in  the  study  of  the  hair  pigments. 

EXPERIMENTS  WITH  GUINEA-PIGS. 
HEREDITY  OF  COAT  COLOR. 

In  the  coat  of  many  mammals  there  occur  two  or  more  distinct  pig- 
ments associated  together  in  the  same  individual  hair,  and  according 
as  one  or  the  other  of  these  predominates  in  particular  regions  of  the 
hair  or  of  the  body,  a  distinct  "  ticking"  of  the  hair  is  produced,  or  a 
color-pattern  of  the  body.  Familiar  examples  of  "  ticked"  or  parti- 
colored hairs  are  those  of  mice,  squirrels,  and  foxes.  Body  color-pat- 
terns of  the  sort  mentioned  occur  in  cats,  tigers,  leopards  and  the  like. 

In  mice  Bateson  (  :  03)*  has  shown  that  there  occur  three  different 
pigments — black,  chocolate,  and  yellow.  In  the  wild  mouse  all  these 
pigments  occur  together  in  the  same  individual  hair,  but  in  fancy  mice 
the  pigments  may  occur  singly  or  combined  in  pairs,  when  they  pro- 
duce the  color  varieties  most  sought  by  fanciers.  Bateson's  observa- 
tions have  been  confirmed  by  Allen  ( :O4). 

COAT  OF  THE  WILD  CAVY. 

In  wild  guinea-pigs  (or  cavies)  occur  the  same  three  pigments  as  in 
mice,  viz,  black,  chocolate,  and  yellow.  A  skin  of  a  young  Cavia  aperea 
Linn,  from  Brazil,  which  lies  before  me,  shows  a  coloration  similar 
to  that  of  the  "  agouti  "  variety  of  the  domesticated  guinea-pig.  On 
the  back  and  sides  of  the  body  the  ordinary  hairs  have  a  tip,  about  2 
mm.  long,  of  a  deep  brownish-black  color.  Below  this  comes  a  yellow 
band  of  about  the  same  length.  The  rest  of  the  hair  appears  black, 
but  is  less  heavily  pigmented  than  the  tip,  and  grows  lighter  toward 
its  base,  which  is  of  a  dull  leaden  color.  Microscopic  examination 
shows  that  the  medulla  of  the  hair,  throughout  its  length,  contains  fine 
pigment  granules  of  an  intense  black  color,  and  associated  with  them 
others  of  a  chocolate-brown  color.  The  former  are  much  more 
numerous  than  the  latter,  and  both  are  much  less  abundant  toward  the 
base  of  the  hair  than  at  its  tip.  The  cortex  of  the  h'air  contains 
throughout  the  greater  part  of  its  length,  where  it  is  relatively  thin,  only 
some  chocolate  pigment  with  a  very  little  black.  But  in  the  distal  part 
of  the  hair  the  cortex  is  much  thicker  and  more  heavily  pigmented. 
Its  terminal  2  mm.  has  the  combination  of  chocolate  and  black  already 
described,  but  in  the  region  just  proximal  to  this  it  contains  only  bright 
yellow  pigment,  which  produces  the  yellow  ticking  of  the  coat. 

The  longer,  so-called  contour  hairs,  found  on  the  back  and  sides  of 
•The  figures  in  parentheses  refer  to  the  Bibliography,  p.  77. 


COAT    CHARACTERS    IN    GUINEA-PIGS    AND    RABBITS.  7 

the  animal,  are  black  throughout  their  length,  lacking  entirely  the 
subapical  yellow  band.  On  the  lower  side  of  the  body  the  hairs  have 
a  pigmentation  similar  to  that  of  the  ticked  hairs  of  the  back,  but  the 
yellow  band  is  longer  and  less  sharply  limited,  and  the  black  tip  is 
inconspicuous,  so  that  the  fur  appears  superficially  of  a  dull  yellow 
color,  but  when  parted  is  seen  to  be  leaden  black  at  the  base. 

COLOR  VARIETIES  OF  DOMESTICATED  CAVY  OR  GUINEA-PIG. 
In  the  various  color  varieties  of  domesticated  cavies  the  same  three 
sorts  of  pigment  found  in  the  wild  animal  exist  singly  or  in  combina- 
tions sometimes  identical  with  those  found  in  the  wild  animal,  some- 
times different. 

AGOUTI. 

In  the  agouti  variety,  of  which  there  are  two  distinct  sub-varieties, 
known  respectively  as  golden  and  silver  agouti,  all  three  pigments  are 
present,  distributed  as  in  the  wild  cavy.  In  the  golden  agouti  the 
pigments  of  all  three  sorts  are  abundant  and  dark,  so  that  the  yellow 
band  becomes  a  red  of  the  sort  found  in  a  sorrel  horse,  while  the 
remaining  portions  of  the  hair  are  fairly  deep  black.  In  silver  agouti 
the  pigmentation  is  less  heavy.  It  may  fairly  be  described  as  a  dilute 
condition  of  the  golden  agouti.  The  yellow  band  is  of  a  pale  yellow 
color,  and  the  black  portions  of  the  hair  are  a  pale  or  bluish  black. 
Silver  agouti  may  be  produced  by  crossing  golden  agoutis  with  albino 
animals  of  a  particular  sort,  as  will  be  explained  presently. 

YELLOW. 

Yellow-coated   varieties,  with    hair   containing   neither   black    nor* 
chocolate  pigment,  are  distinguished  according  to  the  depth  of  their 
color,  as  red,  yellow,  or  cream. 

In  the  lighter  shades,  as  compared  with  the  darker  ones,  the  pigment 
granules  are  smaller  and  possibly  less  numerous.  The  skin  covering 
the  feet  and  ears  of  animals  of  this  variety  contains  chocolate  pigment, 
and,  at  least  in  some  cases,  black  also  ;  the  eye,  too,  certainly  contains 
chocolate  pigment  as  well  as  black,  yet  the  hair,  as  stated,  never  con- 
tains black  or  chocolate  pigment. 

CHOCOLATE. 

Of  the  chocolate  variety  I  have  made  as  yet  a  very  incomplete  study, 
for  lack  of  material.  The  two  animals  which  I. have  had  bore  one  a 
spot  of  red,  the  other  a  spot  of  yellow.  Neither  bore  any  black  hairs. 
The  chocolate  hairs  apparently  contain  no  other  pigment.  Theoretically 
it  should  be  possible  to  obtain  a  chocolate-colored  animal  entirely  free 
from  yellow  as  well  as  from  black  pigment,  as  is  possible  with  mice 
(see  Allen, :  04).  My  experiments  have  not  progressed  far  enough  to 
show  whether  this  expectation  can  be  realized. 


8  COAT    CHARACTERS    IN    GUINEA-PIGS    AND    RABBITS. 

BLACK. 

In  the  black  variety,  black  pigment  predominates  over  the  other  two 
torts  and  obscures  them.  But  I  have  never  been  able  to  obtain  it  in 
a  pure  state.  Chocolate  is  invariably  associated  with  it,  and  usually 
hairs  can  be  found  somewhere  on  the  body  which  show  the  presence 
of  the  red-yellow  pigment  also. 

In  the  ordinary  black  hair  chocolate  pigment  predominates  in  the 
cortex,  black  in  the  medulla.  I  am  unable  to  say  whether  the  red- 
yellow  pigment  is  present  with  them  or  not,  but  I  am  inclined  to  think 
that  in  some  cases  at  least  it  is,  for  here  and  there  on  the  body  one  can 
frequently  find  a  hair  devoid  of  the  black  and  chocolate  pigments,  and 
such  a  hair  commonly  shows  a  red  or  yellow  pigmentation.  Still  there 
are  reasons  for  supposing  that  with  proper  attention  a  black  variety 
could  be  produced  which  would  have  no  red  or  yellow  in  its  coat,  just 
as  red  or  yellow  animals  are  obtained  free  from  black  and  chocolate. 

The  black,  like  the  red-yellow  variety,  occurs  in  forms  more  or 
less  heavily  pigmented,  the  lighter  shades  being  known  as  blue.  The 
latter  can  be  produced  by  crossing  black  animals  with  red  or  yellow 
ones,  or  with  albinos  of  certain  sorts.  Blue  animals  bear  the  same 
relation  to  black  ones  as  silver  agoutis  to  golden  agoutis.  Blue  and 
silver  agouti  are  dilute  forms  of  black  and  golden  agouti,  respectively. 
In  a  blue  animal  the  black  and  chocolate  pigments  are  less  abundant, 
and  the  red-yellow  pigment,  if  it  appears  on  separate  hairs,  is  of  a  light 
(yellow)  shade. 

ALBINO. 

P  The  albino  or  white  variety,  though  apparently  the  simplest  as  re- 
[  gards  pigment  characters,  is  in  reality  the  most  complex.  Albinos 
\  have  pink  eyes,  the  color  of  which  is  due  not  to  a  pigment,  but  to  the 
blood  seen  through  the  transparent  eye.  The  hair  is  likewise  unpig- 
mented  at  birth,  and  may  remain  of  this  character  throughout  life 
over  the  greater  part  of  the  body.  Albino  mice  and  ordinary  albino 
rabbits  apparently  never  develop  pigment  in  any  part  of  their  coat,  but 
such  is  not  the  case  in  cavies.  Though  I  have  carefully  sought  them, 
I  have  never  yet  seen  albino  individuals  which  in  adult  life  did  not 
form  pigment  in  some  region  or  other  of  their  coat.  This  pigment 
makes  its  appearance  first  and  chiefly  at  the  extremities  of  the  body — 
on  the  ears,  the  feet,  and  the  nose — but  may  in  extreme  cases  extend  to 
the  hairs  of  the  body  coat  also.  To  the  unaided  eye  the  hairs  of  the 
extremities  are  of  a  sooty  black  color ;  the  microscope  shows  them  to 
contain  chocolate  pigment,  with  an  occasional  granule  of  black. 

In  the  body  hairs  I  have  in  one  case  identified  reddish-yellow  granules 
without  those  of  other  sorts.  They  are  not  at  all  abundant  and  are 
found  principally  at  the  tip  of  the  hair,  so  that  the  coat  looks  like  an 


COAT    CHARACTERS    IN    GUINEA-PIGS    AND    RABBITS.  9 

ordinary  white  one  which  has  become  dirty.  For  a  long  time  I  so 
accounted  for  the  condition  seen  in  a  particularly  unattractive  albino 
in  my  flock,  but  finding  that  no  change  occurred  in  her  coat,  I  investi- 
gated the  case  with  the  result  noted.  So-called  Himalayan  rabbits 
are  albinos  with  peripheral  pigmentation  similar  to  that  just  described 
for  cavies.  But  there  occur  also  albino  rabbits  without  peripheral 
pigmentation.  In  the  Himalayan  rabbit,  as  in  the  albino  cavy,  the 
coat  of  the  young  is  commonly  white  at  first  all  over  the  body,  but 
soon  becomes  pigmented  at  the  extremities.  In  some  cases  the  first 
coat  on  the  general  body  surfaces  is  slightly  pigmented  also,  the  pig- 
ment being  found  chiefly  in  the  hair  tip.  This  pigmentation  is  already 
forming  at  birth,  and  can  be  recognized  by  the  deeper  red  color  of  the 
skin,  as  compared  with  that  of  normal  individuals. 

I  have  never  seen  a  case  in  which  this  pigmentation  of  the  hair-tips 
persisted  in  the  adult  animal,  though  that  of  the  extremities  regularly 
does.  It  is  apparently  in  rabbits  restricted  to  the  first  coat,  though  in 
guinea-pigs  it  is  found  only  in  the  later  coat. 

It  is  difficult  to  formulate  a  satisfactory  definition  of  an  albino  mammal.  \ 
Absence  of  pigment  is  the  most  obvious  characteristic  of  albinos  ;  yet,  as  / 
we  have  seen,  many  albinos  possess  a  considerable  amount  of  pigment. 
Furthermore,  experiment  shows  that  black-eyed  white  cavies,  which 
produce  no  pigment  whatever  in  the  coat,  nevertheless  transmit  very  dif-^ 
ferent  hereditary  pigment  potentialities  from  those  of  albinos.     Accord- 
ingly the  amount  of  pigment  produced  in  the  coat  is  not  distinctive^ 
between  albinos  and  other  animals ;  neither  is  the  absence  of  pigment 
from  the  eyes  distinctive,  for  Darbishire  ( :  04)  has  experimented  with 
a  race  of  pink-eyed  mice  which  when  crossed  with  albinos  behave 
every  way  like  ordinary  pigmented  ones. 

Without  attempting  a  complete  analysis  of  the  matter,  for  which   J 
present  knowledge  does  not  suffice,  I  would  suggest  the  following  as  / 
criteria  which,  so  far  as  observed,  separate  albino  mammals  sharply/ 
from  all  others.     An  albino  is  an  animal  with  unpigmented  eyes  and\ 
with  little  or  no  pigment  in  its  coat.     The  pigment,  if  present,  is  found/ 
in  greatest  amount  at  the  extremities  of  the  body.     In  a  word,  the  pig-\ 
mentation  of  an  albino  is  essentially  centrifugal.    When  by  selection  OB/ 
cross-breeding  the  pigmentation  is  reduced,  it  is  reduced  centrifugally. 

But  in  animals  not  albinos,  the  pigmentation  is  centripetal.     Reduc-\ 
tion   of  the   pigmented   areas  takes  place  in  this  case  toward  well- ' 
marked  centers,  as  has  been  pointed  out  by  Allen  (  :  04)  in  the  case  of 
mice.     From  a  study  of  spotted  mice  Allen  was  led  to  recognize  for  that 
animal  five  paired  pigment  centers  situated  dorso-laterally,  as  follows : 
(i)  genal  or  cheek  center,  (2)  nuchal  or  neck  center,  (3)   scapular  or 
shoulder  center,  (4)  pleural  or  side  center,  and  (5)  sacral  or  rump  cen- 


10 


COAT    CHARACTERS    IN    GUINEA-PIGS    AND    RABBITS. 


ter.  It  is  possible  that  we  should  recognize  as  a  sixth  distinct  center 
the  retina  of  the  eye.  These  same  centers  are  recognizable  with  great 
clearness  in  the  guinea-pig,  for  in  many  cases  adjacent  patches,  when 
not  separated  by  unpigmented  areas,  contain  elementary  pigments  whose 
limits  are  marked  by  sharp  color  contrasts.  Thus  a  cheek  patch  may 
be  black  and  the  adjacent  shoulder  patch  red  (fig.  5) ;  *  or  the  side  patch 
black  and  the  sacral  patch  red,  or  vice  versa  (figs,  i  and  3) ;  or  again,  the 
right  patch  of  a  pair  black,  the  left  red,  or  vice  versa  (figs.  3  and  6). 
As  compared  with  the  mouse,  the  guinea-pig  shows  slight  differences 
in  the  location  and  extent  of  the  pigment  patches,  as  one  might  expect 


r 


FIG.  i.—  Diagram  showing  the  coat  pattern  of 

973.     Cheek,  side,  and  rump  patches  are 
present,  though  much  reduced  in  extent. 


FIG.  2.—  Coat  pattern  of  O  3166,  a  daughter  of  <j> 
973  (fig.  i).  Cheek  and  rump  patches 
are  present,  but  no  shoulder  or  side 


Each  pair  is  of  a  different  color.  patches. 

in  forms  structurally  so  different.  The  side  patch  of  the  guinea-pig  lies 
chiefly  posterior  to  the  middle  of  the  body  and  frequently  extends  well 
back,  covering  the  greater  part  of  the  hip  and  hind  leg,  while  the 
sacral  patches  may  be  so  small  and  closely  approximated  that  they  seem 
to  form  an  unpaired  area  at  the  extreme  posterior  end  of  the  body  (figs. 
i,  5,  and  7).  The  pigment  patches  are  apparently  not  correlated  with 
internal  structures,  such  as  the  distribution  of  blood  vessels  or  nerves. 
They  are  epidermal  in  origin  and  subject  to  more  or  less  apparent  asym- 
metry and  mutual  displacement,  as  if  they  were  derived  from  distinct 
groups  of  ectodermal  cells  endowed  in  many  cases  with  distinct  pig- 


*In  fig*.  1-8,  solid  black  indicates  black  coat;  black  stipple,  red  coat;  white 
stipple  on  black  ground,  red  and  black  hairs  interspersed. 


COAT    CHARACTERS    IN    GUINEA-PIGS   AND    RABBITS. 


ment  potentialities,  which  by  unequal  cell  multiplication  come  to  cover 
areas  which  may  or  may  not  be  symmetrical  in  arrangement. 

Sometimes  one  or  both  of  a  pair  of  patches  is  wanting  altogether; 
in  other  cases  a  patch  apparently  gets  displaced  from  its  normal  posi- 
tion, so  that  it  lies  across  the  median  plane ;  frequently  when  a  right 
or  left  patch  is  wanting,  its  mate  extends  somewhat  beyond  the  median 
plane  (fig.  3).  Nevertheless,  when  one  examines  a  number  of  spotted 
animals  it  is  clear  that  there  is  a  strong  tendency  for  the  pigmented 
areas  to  occur  in  the  general  body  regions  indicated,  each  of  the  ten 
recognizable  patches  being  a  unit  in  the  composition  of  the  coat. 


FIG.  3. — Coat  pattern  of  ^  1358,  a  son  of  Cj  973 
(fig.  i).  The  right  cheek  patch  is  black, 
the  left  one  red.  There  is  a  left  side 
patch  of  black,  but  no  right  side  patch. 
The  fused  rump  patches  are  red. 


FIG.  4. — Coat  pattern  of  J*  1360,  a  son  of  ^  97; 
(fig.  i).  There  are  cheek  patches  of  red. 
and  a  right  neck  (ear)  patch  of  black, 
No  others  of  the  typical  patches  arc 
present. 


This  unity  may  be  obscured  if  it  happens  that  two  pigments,  as  black 
and  red  for  example,  are  both  present  in  the  same  patch.  Neverthe- 
less, in  such  cases  one  can  often  still  identify  the  typical  patches  either 
by  the  occurrence  of  unpigmented  areas  between  them,  or  by  the 
occurrence  of  mixed  pigments  in  one  patch  and  of  unmixed  pigments 
in  adjacent  patches. 

At  one  time  I  thought  that  I  had  obtained  an  explanation  of  the 
difference  in  behavior  of  the  centrifugal  and  centripetal  types  of  pigmen- 
tation. It  seemed  that  the  centrifugal  pigmentation  was  of  dermal 
origin,  the  centripetal  of  epidermal  origin ;  but  more  careful  examina- 
tion of  sections  of  the  skin  indicates  that  both  sorts  of  pigmentation  are 
similar  in  origin,  arising  within  cells  of  the  epidermis. 


II 


COAT    CHARACTEKS    IN    GUINEA-PIGS    AND    RABBITS. 


SPOTTED. 

The  five  principal  color  varieties  of  the  cavy  which  have  thus  far 
been  described  are  alike  known  as  self-colored  (*.  «.,  colored  alike  all 
over),  in  distinction  from  the  spotted  or  pied  varieties,  which  will  next 
be  noticed.  Each  of  the  four  varieties,  agouti,  black,  chocolate,  and 
yellow  (including  red),  may  become  spotted  with  white  either  by 
reduction  in  the  extent  of  the  pigment  patches  (as  already  explained),  so 
that  they  no  longer  meet  and  cover  the  entire  body,  or  by  the  entire 
absence  of  one  or  more  of  the  typical  color  patches.  The  first-named 
process  produces  such  familiar  manifestations  of  partial  albinism  as  (i) 


FIG.  5.— Coat  pattern  of  J  2698.  The  cheek  patches 
are  of  black,  the  combined  neck  and  right 
shoulder  patches  red  ;  in  the  correspond- 
ing area  of  the  left  side  are  a  few  black 
hairs  mixed  with  the  red ;  the  side  patches 
are  black,  the  minute  rump  patch  mixed 
red  and  black. 


Fie.  6.—  Coat  pattern  of  <j>  1920.  The  left  cheek 
patch  is  black,  the  right  one  red  and 
black  mixed.  The  right  side  and  rump 
patches  are  red,  the  left  ones  black.  A 
sharp  line  of  division  separates  them 
along  the  median  plane  both  dorsally 
and  ventrally. 


a  white  spot  or  a  longitudinal  white  streak  on  the  belly  of  the  animal, 
where  the  side  or  shoulder  patches  fail  to  meet  below,  or  (2)  a  white 
throat,  where  the  cheek  patches  fail  to  meet  below,  or  (3)  a  white 
blaze  (forehead  stripe)  where  they  fail  to  meet  above  (fig.  5),  or  (4) 
white  feet,  to  which  the  shoulder  and  rump  patches  do  not  quite  extend. 
Dropping  out  of  one  or  more  entire  pigment  patches  may  produce  an 
asymmetrical  white  spotting,  such  as  a  white  cheek,  shoulder,  or  side. 
The  two  processes,  reduction  in  extent  of  the  pigment  patches  and 
dropping  out  altogether  of  certain  pigment  centers,  usually  progress 
simultaneously,  and  when  they  occur  symmetrically  may  result  in  such 


COAT    CHARACTERS    IN    GUINEA-PIGS    AND    RABBITS. 


forms  as  the  much  admired  Dutch-marked  varieties,  in  which  the  two 
cheek  patches  are  distinct  (not  united)  above  and  below,  the  shoulder 
patches  are  wanting  altogether,  leaving  a  broad  white  girdle  around  the 
animal,  and  the  rump  patches  fail  to  reach  below  the  middle  of  the 
hind  leg,  though  united  dorsally  (compare  fig.  6,  which  shows  an 
approximation  to  the  Dutch-marked  type). 

A  mottling  similar  in  pattern,  but  with  different  color  effects,  is  pro- 
duced when  the  various  patches  are  differently  colored.  Thus  in  one 
strain  which  I  have  bred  from  the  beginning  of  my  experiments,  some  of 
the  pigment  patches  are  usually  pure  black,  others  pure  red,  though 


FIG.  7. — Color  pattern  of  O  2427.  The  color 
patches  are  of  very  limited  extent. 
They  consist  of  a  red  eye  patch  and  a 
black  neck  (ear)  patch  in  the  right  half 
of  the  body,  and  a  median  (paired,  but 
fused?)  rump  patch. 


FIG.  8.— Color  pattern  of  Cj  2928.  The  left  cheek 
patch  is  red,  the  adjacent  neck  (ear) 
patch  black.  The  fused  right  cheek 
and  ear  patches  are  black.  The  fused 
shoulder  patches  are  of  mixed  red  and 
black. 


occasionally  a  patch  contains  hairs  of  both  colors  intermingled.  (See 
figs.  1-8.)  Further,  the  patches  in  this  strain  frequently  fail  to  cover 
the  whole  body,  so  that  the  animals  are  mottled  with  large  clear  areas 
of  black,  red,  and  white,  a  condition  which  undoubtedly  has  been 
common  among  domesticated  cavies  since  their  introduction  into  Europe 
from  South  America  some  three  or  more  centuries  ago.  (See  Cum- 
berland, p.  n.) 

BRINDLED. 

In  brindled  animals  black  and  red  hairs  are  interspersed  in  the  same 
pigment  patches.  The  latter  may  or  may  not  be  continuous  with  each 
other  ;  if  they  are  not  continuous,  white  mottling  results,  associated 
with  the  brindled  character. 


14  COAT   CHARACTERS    IN   GUINEA-PIGS   AND    RABBITS. 

RUAN,  AND  SILVERED. 

In  roan  animals  white  hairs  are  interspersed  with  red  ones.  A  simi- 
lar modification  may  occur  in  the  coat  of  black  animals  also,  which  are 
then  said  to  be  "  silvered."  I  have  never  seen  a  cavy  with  an  entire 
coat  of  this  character ;  usually  certain  patches  only  are  affected,  or 
more  often  the  ventral  part  only  of  a  patch.  I  have  noticed,  however, 
the  transmission  of  this  character  from  generation  to  generation  and 
have  no  doubt  that  a  roan  race  or  a  silvered  one  could  be  established 
if  desired. 

RESULTS  OF  CROSSING  THE   ELEMENTARY  COLOR  VARIETIES. 
ALBINOS  AND  PIGMENTED  ANIMALS.* 

These  two  types  are  very  distinct.  Each  by  itself  breeds  true,  and 
cross-breeding  between  them  fails  to  produce  intermediates  ;  it  results 
invariably  in  the  production  of  young  of  the  centripetally  pigmented 
type.  Thus  in  the  course  of  these  experiments,  (i)  albino  parents 
mated  inter  se  have  produced  156  young,  all  albinos;  (2)  pure  pig- 
mented parents  (/.  e.,  animals  altogether  devoid  of  the  albino  charac- 
ter) mated  inter  se  have  produced  261  young,  all  pigmented  ;  and  (3) 
albinos  mated  to  pure  pigmented  animals  have  produced  314  young, 
all  pigmented.  The  young  produced  by  this  last  sort  of  mating, 
though  similar  in  appearance  to  those  produced  by  (2),  are  not  pure 
pigmented  animals,  for  they  possess  the  potentiality  to  form  albino 
young,  which  the  young  of  the  two  pure  pigmented  parents  do  not. 
In  Mendelianf  terminology  the  pigmented  character  is  dominant,  the 
albino  character  is  recessive,  and  cross-breds  between  a  dominant  and 
a  recessive  parent  are  hybrid  dominants.  The  hybrids  form  gametes 
(/.  e.,  spermatazoa  and  eggs  ready  for  fertilization),  half  of  which,  ap- 
proximately, transmit  the  pigmented  character,  half  the  albino  character. 

Students  of  heredity  at  the  present  time  are  giving  earnest  attention 
to  testing  the  two  principles  which  make  up  Mendel's  law,  viz,  (i) 
the  principle  of  dominance,  and  (2)  the  principle  of  segregation.  In 
the  case  under  consideration  there  can  be  no  question  of  the  validity  of 
both .  The  centripetal  type  of  pigmentation  invariably  domi  nates  over  the 
albino,  as  the  statistics  already  given  clearly  indicate.  This  is  in  harmony 
with  numerous  observations  on  mice,  rats,  rabbits,  and  other  mammals 
made  by  Haacke  ('95),  Von  Guaita  ('98,  :oo),  Cuenot  (103,:  04), 

^r     *  Although,  as  we  have  seen,  the  albino  guinea-pig  regularly  develops  a  cer- 
/   tain  amount  of  pigment  in  its  coat,  it  will  be  convenient  to  use  the  term 
"albino"  in  contrast  to  "pigmented,"  the  latter  term  referring  only  to  the 
y    dark-eyed  centripetally  pigmented  animals. 

X     t  For  a  brief  statement  of  Mendel's  law,  see  Castle  (  :  03,  or  :  03*) ;  for  a  fuller 
one  tee  Bateson  (:  02). 


COAT    CHARACTERS    IN    GUINEA-PIGS    AND    RABBITS. 


Darbi shire  ( :  04) ,  Castle  &  Allen  (  :  03),  Bateson  (  :  03) ,  Allen  (  :  04) , 
and  others.  The  evidence  that  segregation  of  the  dominant  and 
recessive  characters  occurs  when  the  cross-bred  pigmented  animals 
form  gametes  is  not  less  clear.  The  matter  can  be  conveniently  tested  in 
two  ways :  (i)  By  mating  a  cross-bred  with  an  albino  animal,  when 
half  the  young  should  be  pigmented,  the  other  half  albino,  if  segre- 
gation occurs  as  demanded  by  Mendel's  law ;  (2)  by  mating  hybrids 
inter  se,  when  we  should  expect  three-fourths  of  the  young  to  be 
pigmented,  one-fourth  albino.  The  first  sort  of  mating  has  in  these 
experiments  produced  211  pigmented  and  214  albino  young,  where 
the  expectation  is  212.5  °f  eacn  sort,  which  certainly  is  a  very  close 
approximation.  The  second  sort  of  mating  has  produced  264  pig- 
mented and  112  albino  young,  the  expectation  being  282  pigmented  and 
94  albino  young,  i.  e.,  there  are  18  more  than  the  expected  number  of 
albinos  in  a  total  of  376  young,  a  fairly  close  approximation,  but  not 
so  close  as  that  observed  in  the  first  case. 

Combining  the  results  of  all  matings  which  are  expected  to  produce 
albinos,  we  get  the  following : 


Pigmented. 

Albino. 

Expected 

Observed 

^26 

This  shows  an  excess  over  expectation  of  19.5  albinos  in  a  total  of 
801  young,  or  about  2.5  per  cent. 


$7.1C(.P) 


7.3a 


$7.3* 


?207(?) 

FIG.  9.— A  genealogical  table  showing  the  character,  as  regards  recessive  albinism,  of    the  young  pro- 
duced by  three  matings  between  a  pure  pigmented  (f)  and  a  hybrid  pigmented  animal. 

Matings  of  hybrid  pigmented  with  pure  pigmented  animals  have,  as 
expected,  produced  only  pigmented  offspring,  which  number  35 1 .  The 
Mendelian  expectation  is  that  half  the  young  so  produced  will  be  pure 
in  character,  half  hybrid.  Since  the  two  sorts  look  alike,  only  indi- 
vidual breeding  tests  will  suffice  to  distinguish  them.  In  certain  cases 
such  tests  have  been  made,  the  results  showing  that  the  expectation 
based  on  theory  is  realized. 

Fig.9  shows  the  results  of  three  different  matingsof  this  sort  in  a  single 


l6  COAT    CHARACTERS    IN   GUINEA-PIGS    AND    RABBITS. 

family  of  guinea-pigs.  The  animals  enumerated  were  all  pigmented ; 
those  marked  (/*),  when  mated  with  albinos,  produced  only  pigmented 
young  showing  that  they  were  pure;  the  others  produced  some  albino 
offspring,  when  mated  with  albinos  (or  with  other  hybrid  pigmented 
animals),  showing  themselves  to  be  hybrid  in  character.  In  the  case 
of  one  animal  only  (9  207)  no  test  was  made  as  to  the  production  of 
albino  gametes.  This  animal  was  paired  with  pure  pigmented  mates 
only,  and  the  young  were,  of  course,  invariably  pigmented. 

It  will  be  observed  from  fig.  9  that  pure  9  7  was  mated  with  two 
different  hybrid  males,  viz,  c?  R  and  cf  A.  By  cf  R  she  had  four 
daughters  (9  7.1",  9  7.1",  9  7.1%  and  9  7.1*),  two  of  them  pure  (/>), 
two  hybrid  in  character.  By  cf  A  she  had  two  daughters  (9  7.3* 
and  9  7.3b),both  hybrid  in  character.  In  the  next  generation,  hybrid 
cf  A  was  mated  with  pure  9  7.1°,  producing  in  three  different  litters 
seven  pigmented  young,  which  were  used  as  breeders.  One  of  these 
(9  207)  was  not  tested  for  recessive  albinism,  as  already  stated.  Of  the 
others,  four  proved  to  be  pine,  two  hybrid  in  character.  Altogether 
there  were  among  the  young  indicated  in  the  table  six  pure  individuals, 
six  hybrids,  and  one  of  uncertain  character. 

f    So  far  as  observed,  there  are  no  intermediate  conditions  between  pure 
[  and  hybrid  pigmented  animals.     If  an  animal  forms  albino  gametes  at 
i  all,  half  its  gametes  are  of  that  character.     Of  course  in  individual 
litters,  or  when  only  small  numbers  of  offspring  are  dealt  with,  con- 
siderable deviations  from  the  Mendelian  ratios  are  likely  to  be  encoun- 
tered.    This  is  to  be  expected  on  the  theory  of  probabilities,  as  Allen 
(rcxj,  p.  no)  has  clearly  pointed  out.     But  when  more  extensive  tests 
are  made  the  expected  ratios  are  more  closely  approximated. 

ALBINISM  AND  THE  "LAW  OF  ANCESTRAL  HEREDITY." 
The  foregoing  results  show  very  clearly  that  albinism  conforms 
in  its  mode  of  inheritance  to  Mendel's  law  of  heredity.  The  fact, 
however,  must  not  be  overlooked  that  a  somewhat  different  explanation 
of  its  inheritance  has  recently  been  given,  based  on  Gallon's  "  law  of 
ancestral  heredity."  I  shall  not  at  this  time  enter  into  a  detailed  dis- 
cussion of  Gallon's  hypothesis,  which  was  an  entirely  rational  one  in  the 
form  in  which  it  was  originally  proposed,  and  quite  in  harmony  with  the 
phenomena  of  gametogenesis  as  then  interpreted.  I  have  shown  else- 
where (Castle,  :o3h)  by  a  specific  test  in  the  case  of  mice,  based  on  the 
observations  of  Von  Guaita  ('98,  :oo),  that  Gallon's  law  fails  to  account 
for  the  observed  facts  concerning  the  inheritance  of  albinism,  but  that 
Mendel's  law  does  this  perfectly.  Nevertheless  Darbishire  ( :  04),  like- 
wise dealing  with  albinism  in  mice,  though  admitting  that  certain  of 
his  results  are  not  in  disagreement  with  Mendel's  law,  is  inclined  rather 


COAT    CHARACTERS    IN    GUINEA-PIGS    AND    RABBITS. 


to  interpret  the  phenomena  on  some  such  hypothesis  as  that  of  Galton. 
He  states  the  matter  very  clearly  (p.  24)  as  follows : 

It  is  well  known  that  according  to  this  [MendelianJ  view  the  hybrid  contains 
equal  numbers  of  germ-cells  which  produce  the  dominant  character,  and  of  those 
which  produce  the  recessive;  and  this  is  said  to  be  true  of  the  hybrids  however 
far  the  individual  is  removed  from  the  original  cross,  whether  it  is  the  result  of 
the  cross  (*'.  «.,  the  hybrid)  or  the  great-great-grandchild  of  this.  This  is  the 
ground  on  which  the  doctrine  of  the  purity  of  the  germ-cells  and  the  law  of 
ancestral  heredity  flatly  contradict  one  another;  the  former  asserting  that  DR  x 
DR  will  produce  25  per  cent  DD,  50  per  cent  DR,  and  25  per  cent  RR  for  a 
very  great  if  not  an  indefinite  number  of  generations  ;  the  latter  maintaining  that 
the  further  the  individual  hybrid  under  consideration  happens  to  be  removed  from 
the  cross  the  less  albinos  will  it  produce ;  and  that  two  hybrids  whose  mothers  were 
albinos  will  produce  more  albinos  than  would  two  hybrids  wM  have  no  albinos 
in  their  pedigree  later  than  their  great-great-great-grandmother.  This  seems  to 
me  to  afford  a  case  in  which  experiment  could  provide  a  decisive  answer. 

In  this  statement  I  heartily  concur. 

The  experiment  which  Darbishire  made  was  this.  He  made  three 
different  kinds  of  matings  between  animals  which,  we  are  told,  were 
hybrids,  (i)  In  one  case  each  of  the  two  animals  mated  had  one  albino 
and  one  pigmented  parent.  (2)  In  the  second  case,  one  animal  was  of 
the  parentage  just  described,  the  other  was  born  of  two  pigmented  par- 
ents. (3)  In  the  third  case,  the  parents  of  both  animals  were  pig- 
mented. In  brief,  there  were  two  albino  grandparents  in  case  (i),  one 
albino  grandparent  in  case  (2),  and  no  albino  grandparents  in  case  (3). 
The  ancestry  back  of  the  grandparents  was  the  same  in  all  three  cases. 
The  conditions  are  thus  very  simple  and  should,  as  Darbishire  suggests, 
give  a  decisive  test.  Darbishire  states  that — 


Number  of 
young. 

Number  of 
albinos. 

Albinos 
(percent.). 

121 

3O 

io7 

20 

18  69 

Q-> 

IO 

IO  7? 

This  is  a  seemingly  conclusive  demonstration  of  the  correctness  of 
Darbishire's  contention  ;  but  in  fact  Darbishire's  results,  when  carefully 
analyzed,  prove  just  the  opposite  of  his  deduction. 

Fortunately  he  has  recorded  in  an  appendix  the  various  litters  from 
which  the  totals  given  are  made  up.  An  examination  of  these  records 
makes  it  evident  that  his  so-called  "  hybrids  "  were  not  all  hybrids. 
In  mating  (i)  the  animals  used  undoubtedly  were  hybrids,  since  each 
had,  as  stated,  one  albino  and  one  pigmented  parent.  It  is  noteworthy 
that  in  that  case  the  Mendelian  expectation  of  25  per  cent  albinos  is 


l8  COAT   CHARACTERS   IN   GUINEA-PIGS   AND   RABBITS. 

realized  as  perfectly  as  is  possible  in  an  odd  number  of  young,  there 
being  30  albinos  in  a  total  of  121  young.  In  cases  (2)  and  (3)  Darbi- 
shire gives  us  no  evidence  that  the  animals  which  he  mated  were 
really  hybrids  in  the  sense  that  they  contained  recessive  albinism.  He 
calls  them  "  extracted  hybrids"  because  they  had  dark  eyes,  as  did  all 
his  primary  hybrids  obtained  by  crossing  pink-eyed  with  albino  mice. 
The  latter  unquestionably  were  hybrids  in  the  sense  that  they  con- 
tained recessive  albinism,  for  in  every  case  one  of  the  parents  was  an 
albino.  The  former  may  or  may  not  have  contained  albinism  recessive  ; 
Darbishire's  experiments  indicate  that  in  some  cases  they  did,  and  in 
other  cases  they  did  not.  Darbishire  himself  has  shown  that  there  is 
in  his  mice  (contrary  to  an  erroneous  prediction  of  Castle  &  Allen, 
:  03,  p.  612)  no  necessary  correlation  on  one  hand  between  recessive 
albinism  and  dark  eyes,  and  on  the  other  hand  between  freedom  from 
albinism  and  the  pink-eyed  pigmented-coat  condition.  He  calls  especial 
attention  to  the  fact  (p.  22)  that  in  five  different  families  of  his  mice 
there  occurred  altogether  seven  pink-eyed  pigmented  animals,  which 
in  each  case  had  one  albino  and  one  pigmented  parent,  and  which 
accordingly  must  have  been  hybrids.  In  an  earlier  paper  (Darbishire, 
:  03,  p.  285)  he  showed  that  a  pink-eyed  mouse  of  this  kind  does  pro- 
duce albino  offspring  when  mated  to  albinos,  a  thing  which  his  original 
(pure)  stock  of  pink-eyed  mice  never  did.  If,  then,  pink-eyed  pigmented 
animals  may  contain  recessive  albinism,  is  it  improbable  that  dark- 
eyed  animals  may  in  some  cases  fail  to  contain  it  ? 

Accordingly,  in  what  have  been  called  Darbishire's  matings  (2)  and 
(3),  we  may  reasonably  ask  for  evidence  that  the  animals  mated  were 
really  hybrids.  A  pair  which  has  produced  albino  offspring  consists 
unmistakably  of  two  hybrid  animals.  Pairs  which  fail  to  do  this  are 
questionably  hybrid  and  maybe  provisionally  left  out  of  consideration. 
In  mating  (i)  where  both  parents  were  unquestionably  hybrid,  since 
each  had  an  albino  parent,  Darbishire  gets  the  precise  Mendelian 
proportion  (one-fourth)  of  albinos.  The  question  is,  are  fewer  albinos 
produced  by  hybrids  in  matings  (2)  and  (3),  in  which  the  albino  ances- 
try was  less. 

Omitting  only  pairs  which  failed  to  produce  any  albinos  in  matings 
(2)  and  (3),  Darbishire's  observations  may  be  summarized  as  follows  : 


Pigmented 
young. 

Albino 
young. 

Albinos 
(per  cent). 

Mating  (i)  

Mating  (2)  

24-79 

3I-35 

Mating*  (a)  and  (3)  together. 

79 

30 

27.52 

COAT    CHARACTERS    IN    GUINEA-PIGS    AND    RABBITS.  19 

Instead  of  producing  less  than  25  per  cent  of  albinos,  as  Darbishire 
supposes  them  to  do,  matings  (2)  and  (3)  really  produce  more  than 
that  proportion  of  albinos.  Considered  separately  they  produce,  one 
somewhat  more  than  25  per  cent,  the  other  somewhat  less,  as  we 
should  expect  to  be  the  chance  result  where  small  numbers  of  young 
are  considered. 

In  further  evidence  that  Darbishire's  "  extracted  hybrids  "  did  not  in 
all  cases  contain  recessive  albinism,  his  matings  of  such  animals  with     . 
albinos  are  instructive  (see  his  Table  F,  p.  36).     Five  out  of  nineteen    / 
such  matings  failed  to  produce  any  albinos  whatever,  though  they  pro-    / 
duced  a  total  of  19  young,  all  pigmented.     If  the  pigmented  parents  in 
these  matings  had  really  been  hybrids,  half  their  young  should  have  been 
albinos.     Such  was  precisely  the  proportion  of  albinos  produced  by  the 
fourteen  matings  in  which  the  pigmented  parent,  though  of  the  same 
ancestry  as  in  the  foregoing  cases,  showed  itself  to  be  really  a  hybrid, 
for  these  fourteen  matings  produced  36  pigmented  young  and  36  albinos. 

Darbishire  designates  the  cases  just  discussed  "  the  most  conclusive 
results  which  I  have  obtained  "  [in  favor  of  the  law  of  ancestral  hered- 
ity]. Careful  examination  of  these  results,  however,  as  we  have  seen, 
makes  them  seem  far  from  conclusive  in  favor  of  that  hypothesis.  I 
have,  therefore,  thought  it  worth  while  to  apply  a  further  experimental 
test  to  Darbishire's  hypothesis,  in  the  case  of  guinea-pigs.  » 

In  doing  so  I  class  as  a  hybrid  pigmented  animal  (i)  any  pigmented  \ 
animal  known  to  have  had  an  albino  parent,  or  (2)  any  pigmented  I 
animal  born  of  pigmented  parents  which  has  produced  one  or  more  j 
albino  young.  In  Tables  A  and  B  are  summarized  the  results  of  all  of 
the  matings  between  two  animals  known  to  be  hybrids,  or  between  a 
hybrid  and  an  albino,  which  have  been  made  in  my  later  experi- 
ments. Matings  from  my  earlier  experiments  are  not  included  for 
the  reason  that  the  ancestry  of  the  animals  at  that  time  used  is 
too  imperfectly  known.  The  Mendelian  expectation  is,  as  Darbishire 
states,  that  all  hybrids  alike,  whether  they  have  few  or  many  albino 
ancestors,  will  form  gametes  approximately  half  of  which  bear  the 
albino  character,  half  the  pigmented  character.  Darbishire's  con- 
tention, on  the  other  hand,  based  on  the  hypothesis  of  Gallon,  is 
that  the  more  albino  ancestors  a  hybrid  animal  has,  the  more  albino 
offspring  will  it  produce.  To  test  these  alternative  hypotheses  I  have 
tabulated  the  matings  which  have  been  made  in  these  experiments 
according  to  the  amount  of  albino  ancestry  involved  in  each,  this  amount 
being  greatest  in  the  first  part  of  each  table.  Table  A  includes  matings 
between  two  hybrids,  Table  B  matings  between  a  hybrid  and  an  albino. 


COAT    CHARACTERS    1*    GUINKA-PIGS    AND    RABBITS. 


TABLE  ^.—Proportions  of  albino  young  productd  by  hybrid  pigmented  parents 
of  different  amounts  of  albino  ancestry. 


Albino 
grand- 
parents. 

Albino 
great- 
grand- 
parents. 

Albino 
young. 

Pigmented 
young. 

Remarks. 

a 
a 

6 

4 

9 

2 

"1  Two  albino  grandpar- 
ents, 43  albino  to  124 

2 

3 

3 

4 

\     pigmented    young, 

2 

2 

ii 

2§ 

or  25.9  percent,  al- 

2 

0 

17 

51 

1      binos. 

i 

4 
3 

5 
3 

I 

4 

One  albino  grandpar- 
\     ent,  16  albino  to  18 

[ 

o 

5 
3 

I 

pigmented  young. 

0 

i 

i 

3 

(No  albino   grandpar- 
-      cuts.  6  albino  to  16 

o 

o 

5 

'3 

(     pigmented  young. 

... 

... 

65 

158 

TABLE  B. — Proportions  of  albino  young  produced  by  matings  between  albinos 
and  hybrid  pigmented  animals,  both  with  varying  amounts  of  albinism  in 
their  ancestry. 


Albino 
grand- 
parents. 

Albino 
great- 
grand- 
parents. 

Albino 
young. 

Pigmented 
young. 

Remarks. 

3 

7 

i 

3 

3 

6 

24 

35 

3 

5 

5 

6 

Three   albino    grand- 

3 

4 

10 

9 

parents,    55    albino 

3 

3 

4 

2 

to    64     pigmented 

3 

a 

3 

I 

young. 

3 

i 

3 

I 

3 

o 

5 

7 

J 

6 

i 

3 

5 
4 
3 

2 

8 

21 

8 
16 

3 

20 

8 

15 

Two  albino  grandpa- 
rents, 63  albino  to  56 
pigmented  young. 

0 

9 

7 

5 

2 
I 
O 

0 

4 

2 

7 

3 
3 
3 
9 

One  albino  grandpar- 
ent, 13  albino  to  18 
pigmented  young. 

0 
0 

3 

0 

2 

3 

1 

(No  albino   grandpar- 
•<     ents,  5  albino  to  10 
(     pigmented  young. 

... 

'36 

148 

Throughout  Table  A  we  find  the  expected  Mendelian  ratio  (i  :  3)  of 
albino  to  pigmented  young  approximated,  quite  irrespective  of  the 
amount  of  albino  ancestry  back  of  the  parents  mated.  Of  course,  there 
are  marked  deviations  in  individual  cases  where  the  number  of  young 


COAT    CHARACTERS    IN    GUINEA-PIGS    AND    RABBITS.  21 

is  small,  as  we  expect  on  the  theory  of  probabilities,  but  we  find  no 
falling  off  in  production  of  albinos  as  the  amount  of  albino  ancestry 
decreases. 

Similarly  throughout  Table  B  we  find  the  expected  Mendelian  equality 
of  albino  and  pigmented  young  approximated,  irrespective  of  the  num- 
ber of  albino  grandparents  and  great-grandparents.  Thus  the  proportion 
of  albinos  is  actually  higher  when  there  are  only  two  than  when  there 
are  three  albino  grandparents,  though  on  Darbishire's  hypothesis  we 
should  expect  this  relation  to  be  reversed  ;  for  the  young  produced  in 
cases  where  there  are  three  albino  grandparents  aggregate  55  albino  to 
64  pigmented  animals,  an  excess  of  4.5  pigmented  ;  but  the  young  pro- 
duced in  cases  where  there  are  only  two  albino  grandparents  (in  the  same 
total  number  of  young)  aggregate  63  albino  to  56  pigmented  animals,  an 
excess  of  3.5  albinos.  The  deviations  from  equality  are  in  the  two  cases 
opposite  in  character  and  almost  equal.  Undoubtedly  it  is  merely  a 
chance  outcome  that  they  are  opposite  in  nature  to  what  Darbishire's 
hypothesis  demands.  The  tables  as  a  whole,  however,  do  give  an 
emphatic  negative  to  Darbishire's  position.  They  lend  support  to  the 
alternative  (Mendelian)  hypothesis,  that  any  pigmented  animal  which 
forms  albino  gametes  forms  approximately  50  per  cent  of  such  gametes. 

In  what  precedes  I  have  made  no  mention  of  what  has  been  called 
Pearson's  modification  of  Galton's  law  of  ancestral  heredity.  Else- 
where (Castle,  :  03")  I  have  discussed  this  briefly  in  applying  a  statis- 
tical test  to  the  laws  of  Galton  and  Mendel  in  the  case  of  albinism  in 
mice.  Galton's  law  I  applied  generation  by  generation  to  Von  Guaita's 
('98, :  oo)  mouse  records,  as  Galton  ('97)  himself  had  applied  his  law 
to  the  Basset  hound  records.  The  test  thus  made  showed  the  complete 
failure  of  Galton's  law  as  applied  to  the  heredity  of  albinism.  No  such 
detailed  test  was  made  in  the  case  of  Pearson's  law,  but  the  statement 
was  made  :  "  Comparing  Pearson's  series  with  that  of  Galton  we  see 
that  the  parental  influence  is  reckoned  as  substantially  the  same  by  both 
Galton  and  Pearson,  but  that  Pearson  assigns  a  much  greater  influence 
to  the  more  remote  ancestors  than  does  Galton."  For  which  reason 
it  was  concluded,  "  The  discrepancies  noted  between  observed  and  cal- 
culated [in  testing  Galton's  law]  will  remain  and  even  be  accentuated 
if  we  replace  Galton's  series  with  one  of  those  suggested  by  Pearson. 
For  the  result  will  be  unchanged  [I  should  have  said  similar,  rather 
than  unchanged]  in  Generation  II,  but  the  calculated  numbers  will  in 
most  cases  diverge  still  more  from  the  observed  ones,  in  the  later  gener- 
ations, because  Pearson  attaches  more  weight  to  the  remoter  ancestors 
than  does  Galton."  To  these  conclusions  Pearson  (:  04)  takes  exception, 
maintaining  that  neither  of  the  two  series  which  I  took  from  his  writ- 
ings was  quoted  in  a  form  comparable  with  that  of  Galton's  series. 


COAT    CHARACTERS    IN    GUINEA-PIGS    AND    RABBITS. 


He  gives  a  series  of  his  own  and  that  of  Galton  in  comparable  form. 
They  are,  he  says,  "  if  we  measure  parental  influence  by  intensity  of 
correlation  "  .* 


Influence. 

Pearson's 
series. 

Gallon's 
series. 

| 

} 

i 

i 

j. 

Great-great-grandparental  .  ... 

iV 

A 

Even  when  they  are  given  thus,  it  seems  to  me  still,  as  I  stated 
before,  that  "  Pearson  attaches  more  weight  to  the  remoter  ancestors 
than  does  Galton,"  and  if  so,  that  "  the  discrepancies  noted  between 
observed  and  calculated  [in  testing  Galton's  law]  will  remain  and  even 
be  accentuated  if  we  replace  Galton's  series  with  one  of  those  suggested 
by  Pearson."  That  Pearson  himself  had  not  contemplated  such  a  test 
of  his  law  would  not  affect  in  the  slightest  degree  the  outcome  of  the 
test.  Further,  it  seems  to  me  an  admission  very  damaging  to  a  law  of 
heredity  when  Pearson  says:  "  Personally  I  have  no  means  of  deter- 
mining whether  the  law  of  ancestral  heredity  holds  or  does  not  hold  for 
coat  color  in  mice.  The  theory  has  not  yet  been  worked  out  in  a  form 
covering  Von  Guaita's  cases."  Yet  in  Von  Guaita's  material  we  have 
a  full  record  of  the  coat  color  of  every  animal  in  seven  successive  gen- 
erations, and  we  know  that  back  of  this  for  an  indefinite  number  of 
generations  all  the  ancestors  on  one  side  of  the  ancestry  were  albinos, 
on  the  other  side  spotted  black-and-white.  That  is  sufficient  basis  on 
which  to  make  very  reliable  predictions  as  to  the  character  of  the  off- 
spring, under  Mendel's  law,  as  I  have  elsewhere  shown. 

In  fact,  it  seems  to  me  that  Pearson's  law,  as  he  now  explains  it,  is 
not  a  law  of  heredity  at  a//,  but  one  of  variability  in  successive  gen- 
erations, for  he  says  (p.  no) :  "So  far  as  I  can  understand  the  Law  of 
Ancestral  Heredity  as  I  have  myself  enunciated  it,  the  produce  of  a 
grey  mouse  and  a  fawn  mouse  might  be  on  the  average  a  green  mouse 
without  that  Law  having  anything  to  say  on  the  point.  From  it  you 
can  not  possibly  deduce  what  number  of  the  offspring  of  any  generation 
will  be  like  this  or  that  ancestor.  It  is  not  a  law  of  types,  but  of  the 
distribution  of  deviations  from  type,  and  this  is  a  very  different  thing 
indeed."  But  from  a  genuine  law  of  heredity,  such  as  that  of  Mendel, 
one  is  enabled,  as  I  have  shown,  to  predict  with  great  accuracy  what 
color  types  will  prevail  among  the  offspring  in  successive  generations. 
Since  Pearson's  law,  as  now  interpreted  by  its  author,  though  dealing 
with  alternative  color  types  in  successive  generations,  gives  no  informa- 


COAT    CHARACTERS    IN   GUINEA-PIGS   AND    RABBITS. 


tion  whatever  as  to  what  color  types  will  prevail  in  one  as  compared 
with  another,  nor  as  to  what  proportion  of  the  young  will  be  de-void  of 
color,  it  would  seem  desirable,  to  avoid  confusion,  that  the  law  be  re- 
named as  something  other  than  a  law  of  heredity. 

ALBINISM  AND  SEXUAL  PREPOTENCY. 

Gallon  ('97),  on  purely  empirical  grounds,  was  inclined  to  think 
the  male  sex  prepotent  in  the  transmission  of  black  spots  in  the  case  of 
Basset  hounds.  Though  I  have  elsewhere  (Castle,  :  03")  shown  that 
the  conclusions  which  he  drew  from  that  study  were  probably  erroneous 
because  they  rested  on  false  assumptions,  it  may  be  worth  while  in 
this  connection  to  test  the  idea  of  sexual  prepotency  in  regard  to 
albinism.  This  may  be  done  by  comparing  the  results  of  reciprocal 
matings,  as  shown  in  Table  C,  which  contains  a  summary,  as  regards 
the  production  of  albino  young,  of  most  of  the  matings  made  up  to  this 
time.  Only  matings  between  pigmented  parents  of  undetermined  j 
character  as  regards  recessive  albinism  have  been  omitted  from  this 
summary.  These  omitted  matings  produced  several  hundred  young,  all 
pigmented,  as  was  to  be  expected  if  either  one  or  both  pigmented  parents  / 
were  free  from  recessive  albinism.  From  Table  C  it  is  evident  that,  (i) 
when  a  mating  is  made  between  a  hybrid  pigmented  and  a  pure  pig- 
mented animal  the  result  is  the  same  whether  the  hybrid  be  father  or 
mother ;  in  every  case  the  young  are  pigmented  ;  (2)  when  a  mating 
is  made  between  a  hybrid  pigmented  animal  and  an  albino,  hybrid 
pigmented  and  albino  young  are  produced  in  approximately  equal 

TABLE  C. — Proportions  of  pigmented  (p.)  and  albine  (a.)  young  produced  by 
matings  of  various  sorts. 


Mothers. 

Father  pure 
pigmented. 

Father  hy- 
brid pig- 
mented. 

Father 
albino. 

Young. 

Young. 

Young. 

261    :    o 
136    :    0 
109    :    o 

p,      a, 

215  :      0 
264  :  112 
91  :    98 

/.       a. 

205  :      o 
120  :  116 
o:  156 

Hybrid  pigmented   

Albino 

numbers,  viz,  120  pigmented  to  116  albino  young  when  the  albino 
parent  was  a  male,  91  pigmented  to  98  albino  young  when  the  albino 
parent  was  a  female.  The  deviations  from  equality  are  very  slight 
and  unquestionably  the  result  of  chance.  In  the  one  case  the  deviation  is 
2  individuals  in  a  total  of  236  ;  in  the  other,  it  is  3.5  in  a  total  of  189 
young.  There  is,  accordingly,  in  this  case  no  evidence  of  prepotency 
in  the  transmission  of  albinism  on  the  part  of  either  sex. 


COAT    CHARACTERS    IN    GUINEA-PIGS    AND    RABBITS. 


ALBINISM  AND  LATENT  PIGMENT  CHARACTERS. 

Although,  as  we  have  seen,  (i)  albinism  is  a  condition  recessive  in 
heredity  with  respect  to  ordinary  or  centripetal  pigmentation,  and  (2) 
albinos  produce  only  albino  offspring,  irrespective  of  their  ancestry,  it 
is  not  true,  as  might  be  supposed,  that  one  albino  breeds  like  another 
when  crossed  with  the  same  centripetally  pigmented  type.  This  mat- 
ter has.  been  very  fully  discussed  by  Allen  ( :  04,  p.  130),  but  may  be 
illustrated  by  some  simple  examples,  (i)  My  albino  guinea-pig, 
cf  2002,  when  mated  with  red  females,  invariably  produces  offspring 
marked  with  black  as  well  as  with  red  pigment.  (2)  Albino  c?  635, 
when  mated  with  the  very  same  or  with  similar  red  females,  produces 
young  about  half  of  which  are  pigmented  with  black  and  red,  like  the 
offspring  of  $  2002,  the  other  half  being  pigmented  only  with  red  or 
yellow,  not  with  black.  (3)  Albino  <$  1999,  when  mated  with  red 
females,  produces  only  red  (or  yellow)  pigmented  offspring,  never 
black  pigmented  ones.  From  an  inspection  of  these  three  albino  males 
or  of  their  offspring  by  albino  females,  one  would  get  no  inkling  of  the 
existence  among  them  of  the  differences  revealed  by  the  experiment 
described.  This  experiment  shows  that  in  the  gametes  produced  by 
^  2002,  the  capacity  to  form  black  pigment  is  latent.  This  capacity  is 
exercised  whenever  such  a  gamete  unites  with  one  bearing  the  centri- 
petal type  of  pigmentation.  In  J1  635  only  about  half  the  gametes 
formed  contain  latent  black  ;  in  tf  1999  none  of  the  gametes  formed 
contain  latent  black.  The  idea  underlying  this  explanation  is  that  a 
recessive  character  (in  this  case  albinism)  may  contain  the  dominant 
one  (centripetal  pigmentation)  in  a  state  of  inactivity  which  nothing 
but  cross-breeding  with  the  pigmented  type  will  disturb.  Further  evi- 
dence in  support  of  this  idea  will  be  adduced  when  we  come  to  discuss 
coat  characters  other  than  those  of  pigmentation. 

Meanwhile,  let  me  say  a  word  concerning  the  term  latency.  In  com-\ 
mon  with  others  I  have  frequently  in  earlier  papers  used  this  word  I 
loosely  as  synonymous  with  recessive.  This  usage  was,  I  believe,  an  j 
unfortunate  one ;  accordingly,  in  what  follows  I  shall  use  the  two 
terms  for  conditions  quite  distinct,  which  my  experiments  show  to 
have  a  real  existence  and  to  require  names,  (i)  Recessive  I  shall \ 
use  as  Mendel  used  it,  to  designate  a  character  which  disappears  when  * 
brought  by  fertilization  into  the  same  (hybrid)  individual  with  a  con-  1 
trasted  "  dominant"  character,  but  which  is  transmitted,  distinct  from/ 
the  dominant  character,  in  half  of  the  gametes  formed  by  the  hybrid/ 
individual.  (2)  Latency,  as  I  shall  use  it,  is  a  condition  of  inactivity  \ 
in  which  a  normally  dominant  character  may  exist  in  a  recessive  indi-  j 
vidual  or  gamete.  It  is  questionable  whether  a  recessive  character 


COAT    CHARACTERS    IN    GUINKA-PIGS    AND    RABBITS.  25 

may  ever  be  latent.  Future  investigations  alone  can'decide  this  point. 
A  recessive  character  apparently  reappears  pure  in  half  the  gametes 
formed  by  the  hybrid  dominant  individual,  and  is  present  in  all  the 
gametes  formed  by  a  recessive  individual ;  a  latent  character  apparently 
never  regains  its  existence  apart  from  the  recessive  (i.  e.,  becomes 
active)  until  cross-breeding  brings  this  about.  Future  investigations 
may  require  further  modification  or  even  entire  abandonment  of  these 
definitions,  but  for  the  present  I  find  them  useful  to  express  the  results 
of  my  experiments. 

Latency  of  pigment  characters  in  albinos  is  particularly  clear  in 
mice,  as  shown  by  the  investigations  of  Cu^not  (  :  03),  Darbishire 
(  :  04) ,  and  especially  of  Allen  (  :  04).  For  albino  mice  are,  so  far  as 
known,  wholly  unpigmented,  yet  they  ordinarily,  perhaps  always, 
transmit  latent  pigment  characters,  either  singly  or  in  combinations 
identical  with  those  occurring  in  pigmented  mice.  Alike  in  guinea- 
pigs  and  in  mice,  a  clew  to  what  pigment  characters  are  latent  in  the 
individual  may  often,  though  not  always,  be  learned  from  a  mere 
knowledge  of  its  parentage.  Thus,  in  guinea-pigs,  an  albino  born  of 
two  red  or  yellow  parents  does  not  transmit  latent  black  in  any  of  its 
gametes  ;  but  one  born  of  two  black  parents  may  or  may  not  form 
gametes  transmitting  red  apart  from  black  pigment.  The  reason  for 
this  difference  will  be  apparent  when  we  come  to  consider  the  relation 
of  red  and  black  to  each  other  in  cross-breeding.  For  the  present  I 
would  merely  call  attention  to  this  case  as  showing  that  it  is  not  the 
ancestry  of  the  albinos  which  governs  the  behavior  of  their  gametes  in 
cross-breeding,  as  Darbishire  (  .-04)  maintains,  but  rather  the  existence 
of  pigment  characters  as  distinct  entities,  though  latent,  in  the  gametes 
formed  by  albinos.  In  certain  cases  we  can,  with  confidence,  predict 
the  absence  of  a  pigment  character,  even  in  a  latent  condition,  from 
the  gametes  of  an  albino,  viz,  in  cases  where  we  know  the  pigmented 
parents  to  have  been  free  from  that  character.  Thus  an  albino  born  of 
red  or  yellow  parents  does  not  transmit  black,  because  red  or  yellow 
animals  do  not  contain  the  black  character  either  active  or  latent,  and 
so  can  not  transmit  it  to  their  albino  offspring.  Where  the  parentage 
is  unknown,  suitable  breeding  tests  show  with  equal  certainty  (often  the 
production  of  as  few  as  two  young  indicates  clearly)  what  latent  pigment 
characters  are  transmitted  by  the  albino.  A  particular  pigment  charac- 
ter, when  present  latent  in  the  gametes  formed  by  an  albino,  appears 
to  be  regularly  present  either  (i)  in  all  the  gametes  formed,  or  (2)  in 
half  those  formed,  as  suggested  by  the  cases  of  albino  cfc?  2002  and 
635  already  cited.  No  evidence  exists  of  the  occurrence  of  a  latent 
pigment  character  in  other  proportions  of  the  gametes,  as  should  be 
the  case  on  the  "ancestry  "  idea  of  Darbishire. 


>  COAT    CHAKACTEHS    IN    GUINEA-PIGS    AND    RABBITS. 

INTERCROSSING  OF  DIFFERENT  PIGMENT  TYPES. 
Intercrossing  of  elementary  pigment  types  other  than  albino  results 
not  in  perfect  dominance  of  one  and  complete  disappearance  (recessive- 
ness)  of  the  other,  but  in  coexistence  of  the  two  in  the  offspring,  though 
one  pigment  character  from  its  nature  may  be  much  more  in  evidence 
than  the  other.  Thus  black  animals  mated  with  red  ones  ordinarily 
produce  black  offspring,  though  of  a  shade  different  from  that  of  the 
black  parent,  the  more  intense  black  pigment  masking  to  a  great  extent 
the  presence  of  red.  True  Mendelian  dominance,  then,  is  wanting  in 
such  crosses;  nevertheless  the  other  Mendelian  principle,  segregation, 
is  here  realized. 

THE   AGOUTI   TYPE. 

An  agouti  animal,  as  we  have  seen,  is  one  which  bears  the  three  pig- 
ments— black,  chocolate,  and  red-yellow — in  a  particular  regional  distri- 
bution on  the  same  hair.  It  is  the  original  or  wild  type  of  pigmentation 
and  might  be  expected  to  show  superior  potency  in  crosses.  My  ex- 
periments, which,  however,  are  far  from  complete,  indicate  that  this 
type  of  pigmentation  as  transmitted  in  the  gametes  of  a  wild  animal 
really  is  potent  over  other  types.  Thus,  a  male  Cavia  aperea,  which 
was  captured  wild  in  southern  Brazil,  has  produced  by  two  different 
domesticated  albino  females  (neither  of  which  was  of  agouti-colored 
parentage)  15  young,  all  agouti-colored,  but  in  some  cases  at  least  of  a 
somewhat  lighter  shade  than  the  wild  parent.  I  can  not  speak  very 
emphatically  as  to  the  exact  shade  of  pigmentation  in  several  cases, 
because  all  but  four  of  the  hybrids  were  born  dead,  and  their  coats  have 
been  examined  as  yet  only  in  a  wet  condition.  This  matter  will  be 
discussed  more  fully  in  a  subsequent  paper. 

The  agouti  type  of  pigmentation,  when  borne  by  gametes  of  a  domes- 
ticated guinea-pig,  likewise  shows  a  strong  tendency  to  dominate  over 
other  types  of  pigmentation,  the  only  possible  exception  thus  far  ob- 
served being  black. 

Agouti  x  agouti. — It  goes  without  saying  that  pure  agoutis,  like 
pure*  animals  of  any  other  type,  breed  true.  Thus,  agouti  <$  2017 
mated  with  agouti  9  9  2019  and  2021  produced  6  young,  all  of  the  same 
(golden)  agouti  type  as  the  parents. 

Agouti  x  black. — Agouti  9  2018  mated  with  black  cT  2053  (known 

by  test  to  be  pure)  produced  3  young,  of  which  one  was  an  agouti,  the 

I  other  two  black.     This  outcome  indicates  that  the  black  type  of  pig- 

1  mentation  may  in  some  cases  at  least  have  equal   potency  with  the 

•  The  term  pure  is  here  used,  as  throughout  this  paper,  in  the  Mendelian  sense, 
referring  to  the  character  of  the  gametes  which  an  animal  forms.  Thus  a  pure 
agouti  animal  is  one  which  forms  gametes  all  of  which  transmit  the  agouti  type 
of  pigmentation. 


COAT    CIIARACTEHS    IN    GU1NKA-P1GS    AND    RABBITS.  27 

agouti,  showing  alternative  dominance  with  respect  to  it.  When  this/ 
result  was  obtained  I  at  once  questioned  the  purity  of  9  2018,  suspect- 
ing that  she  might  contain  recessive  black,  but  her  purity  has  since  been 
established  with  considerable  probability  by  a  mating  with  albino  cf  635, 
neither  of  whose  pigmented  parents  was  an  agouti.  This  mating 
produced  4  young,  all  agouti  or  agouti  spotted  with  red.  Previously 
9  2018  had  been  mated  with  agouti  c?  2017,  producing  3  agouti  young. 

Further  support  for  the  idea  that  agouti  and  black  may  show  alter- 
native dominance  is  afforded  by  matings  of  hybrid  agouti  (albino)* 
9  2020.  This  animal  contained  recessive  albinism  in  which  black 
apparently  was  latent.  For,  when  mated  witli  agouti  c?  2017,  she 
produced  2  agouti  and  2  black  young,  indicating  that  at  least  half  her 
gametes  bore  the  black  character,  and  that  this  dominated  over  agouti  in 
at  least  two  out  of  four  cases.  When  mated  with  albino  c?  2039  she  pro- 
duced i  albino,  i  spotted  white  >f  red-black,  and  i  spotted  red-black 
young.  Mated  with  hybrid  red  (albino)  c?  1019,  she  produced  2  black 
>  red  young.  Manifestly  only  part,  if  any,  of  this  female's  gametes 
bore  the  agouti  character,  though  all  apparently  bore  the  character 
black,  either  in  the  agouti  combination  or  in  the  segregated  state. 

Again,  an  agouti  daughter  of  9  2020  by  agouti  c?  2017,  viz,  agouti 
(black?)  9  IO35>  when  mated  with  albino  <$  2059,  produced  2  agouti  > 
red,  and  2  black  >  red  young.  This  result  indicates  that  9  1035, 
like  her  mother,  formed  gametes,  half  only  of  which  bore  the  agouti 
character,  half  the  black  character.  But  the  black  character  is  appar- 
ently present  in  9  1035  as  a  simple  recessive,  not  latent  in  recessive 
albinism  as  in  her  mother  ;  for  the  mating  of  9  1035  with  albino 
cT  2059,  though  it  produced  4  young,  gave  no  albino  offspring ;  and 
a  subsequent  mating  with  white  >  red-black  (albino)  cf  1631  like- 
wise gave  no  albino  offspring,  but  i  agouti  and  i  black-red  young. 
This  9  1035  undoubtedly  arose  from  the  union  of  an  agouti  gamete  fur- 
nished by  the  father  (since  he  was  shown  by  breeding  tests  to  be  pure) 
with  a  gamete  bearing  the  black  character  furnished  by  the  mother, 
9  2020.  But  if  9  1035  does  not  contain  recessive  albinism,  the  gamete 
furnished  at  her  formation  by  9  2020  can  not  have  been  an  albino 
gamete.  It  would  seem  then  that  9  2020  furnished  certain  gametes 
bearing  black,  not  latent  in  association  with  albinism,  but  active.  If  so, 
she  must  have  borne  two  different  pairs  of  contrasted  pigment  poten- 
tialities, viz,  (i)  centripetal  pigmentation  -vs.  albinism;  (2)  agouti 
pigmentation  vs.  black  pigmentation  ;  and  she  must  have  transmitted 

*  A  character  indicated  thus  in  parentheses  is  present  in  a  recessive  condition. 

tThis  symbol  is  used  to  indicate  inequality  in  the  extent  of  body  areas  of 
different  character  as  regards  pigment.  Thus,  white  >  red  means  an  animal 
with  more  white  than  red  fur  on  its  body. 


28  COAT    CHARACTERS    IN    GUINEA-PIGS    AND    RABBITS. 

centripetal  pigmentation  associated  either  with  agouti  or  with  black 
pigmentation  (for  the  latter  combination  9   1035  is  specific  evidence) , 
and  albinism  associated  probably  either  with  agouti  or  with  black  pig- 
mentation (these  of  course  being  in  a  latent  condition).     It  seems  from 
I  this  and  other  similar  cases  that  the  regional  distribution  of  pigments 
I  on  the  body  (centripetal  vs.  albino)  is  something  inherited  independ- 
\  ently  of  the  specific  character  of  the  pigments  formed.     Albinism 
vs.  centripetal  pigmentation  forms  one  pair  of  alternative  (Mendelian) 
characters ;    agouti  vs.  black   pigmentation  forms  another  pair.     An 
animal  like  9  2020,  then,  is  a  dihybrid  as  regards  pigment  characters, 
and  should  form  in  equal  number  gametes  of  four  different  sorts,  viz, 
albino  [black  latent],*  albino  [agouti  latent],  centripetal  agouti,  and 
centripetal  black.     This  idea  is  supported  by  Allen's  (  :  04)  observations 
on  mice,  and  finds  frequent  illustrations  in  these  experiments. 

Agouti  x  red. — I  have  made  this  mating  between  pure  parents  only 
once.  Agouti  9  2019,  mated  with  red  cT  2054,  produced  4  young,  3  of 
them  agouti  >  red,  I  red  >  agouti  >  white.  This  result  indicates  a 
tendency  of  agouti  to  dominate  over  red,  or  at  least  to  mask  the  presence 
of  red.  In  this  experiment,  the  mother,  9  2019,  had  a  red  hip  patch. 
The  occurrence  of  red  and  of  white  spots  on  the  young  was  probably 
due  to  a  mosaic  character  of  certain  of  her  gametes  rather  than  to 
some  peculiarity  of  the  father,  a  self  red. 

One  of  the  young  produced  by  this  cross,  viz,  agouti  >  red  9  1294, 
when  mated  with  her  red  father,  c?  2054,  produced  6  young,  2  agouti 
>  red,  i  red  >  agouti,  2  red-black,  and  i  red,  indicating  segregation  of 
the  respective  agouti  >  red,  and  red  characters  brought  together  in  the 
previous  generation,  so  as  to  allow  of  the  formation  of  pure  red  gametes. 
The  occurrence  of  two  red-black  young  indicates  that  in  some  cases 
the  agouti  character  may  break  up  into  isolated  black  and  red  under 
the  influence  of  the  cross. 

/"     Agouti  x  albino. — Pure  agoutis  mated  with  albinos  of  spotted  or  of 

I    unknown  ancestry  have  produced  only  animals  predominantly  agouti- 

l    colored,  though  the  offspring  have  in   some  cases  had  one  or  more  of 

V  the  typical  color  patches  red  or  white,  but  never  black  or  chocolate. 

The  spotting  with  red  or  white  was  inherent  in  the  agouti  stock  used. 

It  is  probable  that  in  no  case  did  the  albino  parent  in  these  crosses 

transmit   latent   agouti.      This  statement  is  based  on  the  results  of 

other  crosses  made  with  these  same  albino  animals,  as  well  as  on  an 

examination  of  their  pedigrees.     If  this  assumption  is  correct,  there  is 

I  seen  in  this  experiment  a  strong  tendency  for  the  agouti  character  to 

I  dominate  over  other  pigment  characters  contained  latent  in  albino  gam- 

\  etes;  for  every  one  of  the  17  young  was  agouti-pigmented. 

•Brackets  will  be  used  to  indicate  latent  characters,  just  as  parentheses  to 
indicate  recessive  ones. 


COAT    CHARACTERS    IN    GUINEA-PIGS   AND    RABBITS.  29 

The  matings  made  and  their  results  are  : 


Parents. 

Young. 

Gold,  agouti. 

Albino. 

Agouti. 

Agouti- 
red. 

Agouti 
red- 
white. 

Silver 
agouti- 
yellow- 
white. 

Agouti  9  1030  
Agouti  >  red  9  IO29 
Agouti  rf  2017  
Agouti  ¥  2018  

rf  2059... 
$785  

2 

3 
i 

3 
3 

2 

i 

i 

Agouti  >  red  $  202  1. 
Total   

^63S  

6 

9 

i 

i 

That  an  albino  may  transmit  latent  agouti  is  shown  unmistakably  by 
the  following  case.  Albino  c?  2060  was  purchased  from  a  breeder  and 
his  ancestry  is  wholly  unknown  to  me.  But  I  found  on  mating  him 
with  spotted  females  not  of  agouti  parentage  that  a  large  proportion 
of  his  young  were  agouti-marked,  and  this  proportion  proves  to  be 
almost  exactly  one-half.  Thus  he  has  produced  by  15  different  females, 
which  were  spotted  with  black  and  red  (and  in  some  cases  also  with 
white),  19  young  marked  with  agouti  (in  no  case  with  solid  black  hairs 
on  the  body,  though  frequently  with  red  or  white  ones)  and  18  young 
marked  with  black  but  not  with  agouti.  By  the  red  or  red-white 
females  he  has  produced  3  agouti-marked  and  3  black-marked  young. 
The  total  pigmentecl  young  produced  by  matings  with  the  spotted 
females  are  22  agouti-marked  and  21  black-marked,  an  approximation  to 
equality  as  close  as  is  possible  with  an  odd  number  of  young.  The 
matings  with  red  and  red-white  females  show  that  all  the  gametes 
formed  by  c?  2060  bear  the  latent  character  black  pigmentation,  but 
that  half  his  gametes  transmit  it  in  the  agouti  combination  with  red, 
half  in  the  form  of  solid  or  segregated  black. 

If  this  interpretation  is  correct  it  should  be  possible  by  suitable  mat- 
ings of  cJ1  2060  with  his  descendants,  or  of  the  latter  inter  se,  to  obtain 
albinos  all  of  whose  gametes  would  transmit  latent  agouti.  This  mat- 
ter, it  is  hoped,  can  soon  be  given  an  experimental  test. 

In  the  foregoing  case  it  seems  necessary  to  assume  the  dominance  of 
agouti  pigmentation  over  the  intermingled  condition  of  black  and  red 
spots  ;  indeed,  all  my  experiments  support  that  idea,  except  possibly 
those  mentioned  in  discussing  the  agouti  x  black  cross  (p.  26).  The 
alternative  dominance  which  may  have  occurred  in  those  cases  is 
apparently  exceptional,  the  rule  being  that  agouti  pigmentation  domi- 
nates over  black  or  black-red.  Alternative  dominance  can  scarcely  be 
invoked  to  explain  the  results  obtained  from  the  matings  of  c?  2060, 
for  it  would  fail  to  account  for  the  black-red  offspring  in  the  matings 
with  red  or  red-white  females. 


3O  COAT    CHARACTERS    IN    GUINEA-PIGS    AND    RABBITS. 

The  following  experiment  likewise  bears  upon  the  point  which  is 
under  discussion.  Agouti  <?  2017,  mated  with  albino  9  785,  produced 
3  agouti  and  i  agouti  >  red  young  (as  stated  on  p.  29).  The  albino 
9  785  was  born  of  albino  parents,  but  part  of  her  grandparents 
and  great-grandparents  were  spotted  black-red-white,  part  of  them 
albinos;  none  were  agouti-marked.  It  seems  probable,  therefore, 
that  the  pigment  characters  latent  in  the  gametes  of  9  785  were  in 
everv  case  black-red.  If  so,  her  agouti  young  should  contain  recessive 
white  with  which  black-red  had  been  introduced  as  a  latent  constit- 
uent, and  should,  as  explained  on  page  28,  form  in  equal  numbers 
gametes  of  four  sorts,  viz,  agouti,  black-red,  albino  [agouti  latent], 
albino  [black- red  latent].  If  two  such  sets  of  gametes  be  combined 
(as  in  mating  these  hybrid  young) ,  and  all  gametic  unions  prove  equally 
fertile,  their  young  should  be,  on  the  hypothesis  that  agouti  is  dominant 
over  black-red,  in  the  proportions  9  agouti  to  3  black-red  to  4  albino; 
but  on  the  hypothesis  that  agouti  and  black-red  are  alternatively  domi- 
nant, the  young  should  be  in  the  proportions  6  agouti  to  6  black-red  to  4 
albino.  That  is,  on  one  hypothesis,  agouti  young  should  be  three 
times  as  numerous  as  black-red  ;  on  the  other  hypothesis,  both  sorts 
should  be  equally  numerous.  The  result  observed  is  7  agouti  to  3  black- 
red  to  3  white,  which  certainly  favors  the  hypothesis  that  agouti  domi- 
nates over  black-red,  though  the  number  of  young  is  undesirably  small. 

The  details  of  the  experiment  follow  : 


Young. 

Agouti. 

Black-red. 

Albino. 

Agouti  cf  1509  X  Agouti  2  1508  
Agouti  $  1509  X  Agouti  9  1  507  •  •• 

3 

2 

2 

3 

Agouti  cf  1509  X  Agouti  >  red  9  1510.. 

2 

0 

Total   

Other  matings  of  agouti  cf  1509  support  the  hypothesis  that  agouti 
gametes  dominate  over  black-red  ones.  Thus  he  was  mated  with  three 
different  albino  females  derived  from  the  same  black-red-white  spotted 
stock  as  his  mother.  The  gametes  of  these  females  undoubtedly  trans- 
mitted the  black-red,  never  the  agouti  character.  On  the  hypothesis 
that  agouti  is  dominant  over  black-red,  the  young  produced  by  these 
matings  should  be  in  the  proportions,  2  agouti  to  2  black-red  to  4  albino  ; 


COAT    CHARACTERS    IN    GUINEA-PIGS    AND    RABBITS.  3! 

on  the  hypothesis  of  alternative  dominance  between  agouti  and  black- 
red,  the  young  should  be  in  the  proportions,  i  agouti  to  3  black-red  to  4 
albino.  The  numbers  observed  are  2  agouti  to  3  black-red  to  5  albino — 
too  few  to  be  conclusive,  but  favoring  the  former  hypothesis.  On  the 
whole  it  seems  highly  probable  that  agouti  as  a  rule  dominates  over 
all  other  pigment  combinations,  but  in  the  case  of  exceptional  animals 
like  ?  2020,  page  27,  black  or  black-red  gametes  may  be  formed  which 
have  a  potency  equal  to  that  of  agouti.  This  is  an  indication  of  indi- 
vidual prepotency  like  that  discussed  further  on,  under  the  heading, 
"  Prepotency  and  Dominance." 

Agouti  synthetically  produced. — An  occasional  animal  with  an  ex- 
cellent agouti  coat  may  result  from  mating  a  red  with  a  black  individual. 
One  such  animal,  $  1178,  tested  as  to  the  character  of  its  gametes,  ap- 
parently forms  pure  red  and  pure  black  gametes  in  approximately  equal 
numbers,  for  mated  with  red  females  he  has  produced  3  red,  2  black, 
and  i  agouti  young.  His  red  gametes  uniting  with  those  furnished  by 
the  red  females  should  produce  red  offspring,  while  his  black  gametes 
forming  similar  unions  should  produce  either  black  or  agouti  young. 
Hence  the  result  observed  is  exactly  what  we  should  expect,  on  the 
hypothesis  that  black  and  red  have  formed  merely  a  temporary,  not  a 
permanent  union  in  the  agouti  parent,  and  that  the  gametes  formed  by 
it  contain  either  red  or  black,  but  not  the  two  united  in  the  agouti  com- 
bination. What  conditions,  if  any,  can  bring  about  a  permanent  union 
between  segregated  red  and  black  my  experiments  do  not  as  yet  indicate. 

THE    BLACK   TYPE. 

My  original  black  animals  were  obtained  from  Miss  Soule.  Bred 
inter  se  they  produce  only  black  offspring,  though  a  few  red  hairs 
may  usually  be  found  by  careful  search  somewhere  on  the  body.  The 
relation  of  black  to  agouti  has  already  been  discussed,  so  that  we 
may  pass  immediately  to  its  relations  with  red  and  with  albinism. 

Black  X  red. — The  young  produced  by  this  cross  have  ordinarily 
a  black  coat,  but  of  a  reddish  shade,  as  if  the  pigmentation  of  the  black 
parent  had  been  diluted  with  that  of  the  red  one  ;  in  other  words,  the 
characters  of  both  parents  show  their  influence  in  the  offspring,  which 
are  not  intermediate,  only  because  black  pigment  is  so  much  more 
opaque  than  red  that  the  latter  is  scarcely  visible.  In  other  cases  the 
weakening  of  the  black  pigmentation  is  seen  in  a  restriction  of  the 
black  pigmented  areas,  which  then  fall  into  the  series  of  pigmented 
patches  described  on  page  9,  while  red,  or  red  and  white  together,  fill 
up  the  intervening  spaces.  This  results  in  the  production  of  a  black- 
red  or  black-red-white  spotted  animal.  Or,  thirdly,  and  less  often 
still,  the  black  and  red  may  have  the  characteristic  distribution  which 
produces  the  agouti  coat. 


i 


\ 


COAT    CHARACTERS    IN    GUINKA-PIGS   AND    RABBITS. 


In  detail,  the  matings  which  I  have  made  under  this  category  and 
their  results  are  as  follows : 


Young. 

Parents. 

Reddish 
black. 

Black  > 
red. 

Agouti. 

$  2053  (black,  but  with  a  few  red  hairs) 

2 

y  2013  (very  deep  black,  without  red 

2 

i 

Total 

2 

6 

i 

Hybrids  of  all  three  sorts  show  segregation  in  forming  gametes,  though 
as  yet  not  exactly  in  the  expected  Mendelian  proportions.  Thus  the 
two  reddish-black  young  of  9  2013  by  J*  2054,  viz,  9  1 179  and  cT  1 180, 
have  given  the  following  results  when  mated  with  red  animals  : 


Young. 

Parents. 

Red. 

Yellow. 

Black- 
red. 

Black- 
yellow. 

Agouti. 

Black  9  "79  X  red  $  2054 
Cfatherof  $  1179)  

2 

i 

2 

Black  9  1179  x  red  <^  2004. 

2 

... 

2 

Black  cP  ubo  x  red  P  1073. 

3 

... 

4 

... 

Black  c?  1180  X  red  9  1278- 

3 

... 

Black  rfj  1180  X  red  V  1279- 

i 

2 

i 

Black  J1  1180  X  red  9  1286. 

2 

... 

...' 

Black  cf  1180  X  red  Q  n°7- 

4 

... 

... 

Black  <$  1  180  x  red  9  2026. 

2 

I 

i 

Black  g  1180  x  red  9  2027. 

s 

I 

... 

- 

Total  

24 

i 

2 

t 

2 

8 

• 

12 

It  will  be  observed  that  9  1 179  has  given  by  two  different  red  males 
as  close  an  approximation  as  is  possible  to  the  expected  equality  of 
red  young  on  one  hand  and  of  black  or  agouti  young  on  the  other 
hand.  But  her  brother,  c?  1180,  has  produced  a  most  astonishing 
excess  of  red  individuals,  more  than  three  times  as  many  red  young 
being  recorded  as  black  ones.  It  would  seem  to  be  a  peculiarity  of 
this  animal  to  form  red  gametes  either  more  numerous  or  more  vigorous 
than  his  black  ones,  for  red  young  are  in  excess  in  all  his  matings 


COAT    CHARACTERS    IN    GUINEA-PIGS    AND    RABBITS. 


except  one,  that  with  9  1073.  Another  unexpected  result  is  the  pro- 
duction of  weakly  pigmented  animals  of  the  red  type,  i.  e.,  of  yellows, 
and  of  one  yellowish-black  (or  blue)  individual,  where  we  expect  only 
red  and  reddish-black  offspring.  The  first  mentioned  peculiarity  of 
cT  nSo  is  possibly  shared  by  other  cross-breds  between  the  black  and 
red  types.  Thus  black  >  red  9  1156,  a  daughter  of  black  cf  2053  by 
red  9  755,  gave  the  following  result : 


Parents. 

Young. 

Red. 

Agouti. 

9  1156 
9  1156 

X  red  c 
X  red  c 

f'  2054  

i 
4 

o 

P  2004  

Again,  reddish-black  9  3OI7'  a  daughter  of  the  similarly  pigmented 
9  1 179  by  red  J1  2054,  gave  by  red  c?  2004,  three  young,  all  red.  The 
results  thus  far  obtained  by  mating  with  red  females  the  agouti  d"  1178 
(produced  by  the  cross  of  black  with  red)  have  been  previously  given. 
Thev  indicate  that  this  hybrid  forms  red  and  black  gametes  in  num- 
bers approximately  equal.  Combining  the  results  of  all  the  matings 
made  between  an  animal  whose  parents  were  red  and  black  respec- 
tively, and  red  animals,  we  get  37  red  (or  yellow)  to  14  black,  blue,  or 
agouti,  where  we  should  expect  an  equal  number  in  each  of  the  two 
general  classes.  Further^  experiments  are  needed  to  show  whether 
the  inequality  thus  far  observed  is  a  chance  result  which  will  disap- 
pear with  larger  numbers,  or  whether  it  is  significant  and  will  remain. 

Several  other  black-red  animals,  which  evidently  contain  recessive 
red,  have  produced,  when  mated  with  red  animals,  8  black-red  and  13 
red  young.  The  matings  making  up  this  total  are  as  follows : 


Parents. 

Young. 

Black-red. 

Red. 

Black-red. 

Red. 

cf  23  
c?  23 

9  4  

0 

o 
o 

4 
i 
i 
i 

2 

3 

9  1227...  . 
9  1288...  . 
9  1448-.  - 
5  1482...  . 
9  1607...  . 
cT  "65...  . 

Total.... 

$  1140  .  .. 

CJ"  1140.  .. 
$  1140.  .. 

3  1140  .. 

qf  1140.  .. 
9  1262.  .. 

8 

'3 

34 


COAT    CHARACTERS    IN    GUINEA-PIGS    AND    RABBITS. 


Again,  black-red  pigmented  animals  which  contain  recessive  red 
(or  else  latent  red,  see  p.  25)  when  mated  inter  sc  have  produced 
young  as  follows : 


Younj 

I- 

Black- 
red. 

Red. 

Albino. 

Black-red  cf  23  x  black  red  (albino)  9  i  A      

Black-red  (albino)  d"  89.  i"  x  black-red  (albino)  $  i  A. 
Black-red  rf  23  x  black  red-white  9  51  2b  

2 

• 

Black-red  (albino)  j*  89.1*  x  black-red-white  9  51.2*. 
Black-red  (albino;  cf  89.  I*  X  black-red  (albino)  9  89.  3s. 
Black-red  c?  23  x  black-red  (albino)  9  §9  3b  

4 

i 
6 

• 

Black-red  c?  23  x  black-red-white  9  2°9  

i 

j 

Total  

22 

I  I 

i 

We  should  expect  the  black-red  young  to  be  three  times  as  numerous 
as  the  red  ones,  but  we  find  them  only  twice  as  numerous,  yet  the 
numbers  involved  are  small,  and  the  precise  proportion  observed 
probably  not  significant.  Combining  the  results  of  all  matings  of 
black  pigmented  animals  which  are  expected  to  produce  red  young 
we  get  a  total  of  105  young  :* 


Black  pig- 
mented. 

Red  pig- 
mented. 

Observed         

61 

Expected       

61 

Black  X  albino. — As  elsewhere  stated,  few,  if  any,  of  my  black 
animals  are  entirely  free  from  red  pigmentation,  and  my  albinos,  so  far 
as  determined,  always  possess  latent  red.  Accordingly,  more  often 
than  otherwise,  the  young  produced  by  this  cross  show  more  or  less 
red  pigmentation,  though  in  my  experiments  it  has  never  amounted  to 
more  than  a  few  red  hairs,  or  one  or  two  small  red  spots  situated  at  the 
border  of  one  of  the  typical  pigment  patches.  The  blackest  young 
produced  in  this  series  of  experiments  resulted  from  matings  between 
a  very  heavily  black  pigmented  female  (9  2012)  and  an  albino  male 
(c?  635)  part  of  whose  gametes,  as  stated  on  page  24,  entirely  lacked 
the  black  character. 


*  Further  experiments  made  since  the  foregoing  was  written  continue  to  give 
a  steady  excess  of  red  animals  and  a  corresponding  deficiency  of  black  ones. 


COAT    CHARACTERS    IN    GUINEA-PIGS    AND    RABBITS.  35 

In  detail,  the  matings  made  are  as  follows : 


Young. 

Mating. 

Parents. 

Black. 

Black  *> 
red. 

Black  > 
white. 

(i) 

Black  9  2O12  x  albino  (^635  

7 

i 

i 

(2) 

Black  Q  2012  x  albino  $  2002... 

2 

2 

(3) 

Black  V  2014  x  albino  ^2039.... 

.. 

3 

... 

(4) 

Black  9  2014  x  albino  $  2059.... 

3 

... 

fsb 

Black  >red  $  2053  x  albino  9  807 

4 

... 

(6) 

Black  >red  tf  2053  x  albino  9  ?66 

5 

... 

Total  

7 

18 

•j 

The  relation  existing  between  the  characters  combined  in  this  cross 
is  one  of  simple  Mendelian  dominance,  followed  by  segregation  in  the 
next  generation,  as  is  clear  from  the  following  matings : 


Mating. 

Parents. 

Young. 

Black. 

Black  > 
red. 

Black  > 
white. 

Albino. 

(7) 
(8) 
(9) 

Black>white  J*  1  1  1  1  [born 
of  mating  (2)  above]  X 
albino  9  9  

4 
3 

2 

4 

i 

9 

4 
6 

Black>red  $  I256  [born 
of  mating  (6)  above]  x 
albino  9  9 

Black  $  1570  [born  of  mat- 
ing (i)  above]  X  albino 

Q  O 

6 

Total 

6     - 

9 

5 

19 

20 

The  hybrid  males,  it  is  evident,  form  in  approximately  equal  num- 
bers albino  gametes  and  those  bearing  the  centripetal  type  of  pigmen- 
tation, and  the  latter  transmit  essentially  the  same  kind  of  pigmentation 
as  was  possessed  by  the  pigmented  parent  and  the  pigmented  grand- 
parent. This  conclusion  is  further  supported  by  the  result  of  matings 
of  hybrids  inter  se,  as  shown  on  the  following  page. 


COAT    CHARACTERS    IN    GUINEA-PIGS    AND    RABBITS. 


ParenU. 

Young. 

Black. 

Black> 
red. 

Black  > 
white. 

Albino. 

Black>red  <?  I2s6  [mating  (6)1  x 

black>red  ?  1194  [mating  (5)]  

3 

... 

... 

... 

Black>red  $  1256  [mating  (6)J  X 

black>red  9  "96  [mating  (5/j  

i 

3 

... 

2 

Black>red  $  1256  [mating  (6)]  X 
black>red9i255  [mating  (6)]  
Black  rf  1570  [mating  (i)]  x  black> 
red  9  1194  [mating  (5)]  
Black  rf  1570  [mating(i)]x  black  > 
red  y  UQ7  [mating  (5)]  . 

2 

2 
j 

... 

I 

Black  tf  1570  [mating  (i)x  black  > 

I 

2 

I 

Black  tf  1570  [mating  (i)]  X  black> 

Total                  .             

6 

6 

18 

The  result  observed  is  in  exact  agreement  with  the  expected  Men- 
delian  ratio,  3:1. 

From  what  was  said  on  page  24  concerning  the  transmission  of  pig- 
ment characters  by  albino  gametes,  we  should  expect  that  the  charac- 
ter of  the  albino  used  in  a  cross  with  black  would  in  some  measure 
influence  the  result  of  the  cross.  That  this  is  actually  so  is  indicated 
by  comparing  results  of  matings  (i)  and  (2),  page  35,  the  black  parent 
being  the  same  in  both  matings,  but  the  albinos  markedly  different. 
One  of  the  albino  males  (<$  635)  forms  gametes  about  half  of  which 
are  entirely  free  from  black  ;  the  other  (c?  2002)  always  transmits  black 
pigmentation,  frequently  with  a  tendency  to  spotting.  By  the  former 
were  produced  nine  young,  all  but  two  of  which  were  self-colored  black  ; 
by  the  latter  were  produced  four  young,  all  spotted  with  red  or  black. 

THE    RED    TYPE. 

Red  (including  its  dilute  forms  known  as  yellow  and  cream)  is  the 
only  one  of  the  three  pigments  of  the  coat  which  I  have  been  able  to 
obtain  unquestionably  free  from  the  other  two.  Red  and  yellow  ani- 
mals not  only  form  no  black  pigment  in  their  hair,  but  appear  to  be 
incapable  of  transmitting  the  capacity  to  form  black  coat  pigment.  Red 
animals  mated  inter  se  ordinarily  produce  only  red  offspring,  but  reds 
obtained  by  cross-breeding  with  black  may  produce  yellows  when  bred 
inter  se.  This  case  will  receive  further  attention  presently.  Yellow 
mated  with  yellow  produces,  in  my  experience,  only  yellow  offspring. 

The  relations  of  red  to  agouti  and  to  black  have  already  been  dis- 
cussed, and  in  part  also  that  of  red  to  albinism.  Accordingly  it  remains 
only  to  consider  in  greater  detail  the  last-named  topic. 


COAT    CHARACTERS    IN    GUINEA-PIGS    AND    RABBITS.  37 

Red  X  albino* — The  result  of  this  cross  depends  upon  what  latent 
pigment  characters  are  borne  by  the  albino,  and  this  in  turn  may  in 
some  cases  be  inferred  from  the  ancestry  of  the  albino,  though  in  other 
cases  not.  Most  of  the  albinos  with  which  I  have  experimented  contain 
latent  black  as  well  as  red,  and  when  mated  with  red  or  yellow  animals 
produce  invariably  black-pigmented  offspring.  The  matings  indicated 
in  Table  D  fall  into  this  category  of  cases. 

TABLE  D. — Matings  of  albinos  (all  of -whose  gametes  transmit  latent  black)  -with 
red  or  yellow  animals.      The   pigmented  offspring  all  have   black  pigment 


in  (heir  coats. 


Parents. 

Young. 

Albino. 

Pure  red  or 
yellow. 

Black- 
red. 

Black- 
yellow. 

Gold 
agouti- 
red. 

Silver 
agouti- 
yellow. 

Albino  9  644..    . 
Albino  S  76i  
Albino  9  778  
Albino  9  778..  . 
Albino  $  779  
Albino  9  1216  ... 
Albino  9  1649  ••• 
Albino  cf  2002 
Albino  $  2002... 
Albino  <-f  2002... 
Albino  ,-^  2039... 
Albino  ^  2039... 

Total  

Red  (^  2004  

4 

2 

3 

I 
4 
3 

2 
I 

•• 

Red  cf  2004  

Red  $  2004  
Red  $  2054  •  
Yellow  J*  1347-  • 
Red  9  755  
Red  9  784  
Yellow  9  2001... 
Red  9  753  
Red  9  830  

4 

2 

3 

2 

4 

4 

28 

8 

3 

i 

Albino. 

Hybrid  red  or 
cream  (albinism 
recessive). 

Black- 
red. 

Black- 
yellow. 

Gold 
agouti- 
red. 

Silver 
agouti- 
yellow. 

i 

2 
< 

4 

i 
4 

Albino  9  "Him- 
alayan." 
Albino  9  766.... 
Albino  9  1027... 
Albino  9  1028... 
Albino  9  I544--- 
Albino  <$  2002  ... 
Albino  (^  2039... 
Albino  tf  2060  .. 
Albino  3"  2060... 
Albino  (^  2060... 

Total 

Cream  ^  1147.... 
Cream  $  1147.... 

2 

3 

i 

... 

... 

Red  (j*  1019  

2 

... 

2 

Red  9  683 

2 

Red  Q  1020  
Red  Q  i"*cc 

I 

I 
2 

'.'.'. 

2 
I 
2 

4 

Red  9  1442  
Red  9  1476  

3 

10 

4 

5 

... 

19 

Sixteen  different  albinos  mated,  as  indicated  in  the  table,  with  red, 
yellow,  or  cream  animals,  produced  59  pigmented  young,  all  bearing 
black  pigment. 


33 


COAT    CHARACTERS    IN    GUINEA-PIGS    AND    RABBITS. 


/  Seven  of  my  albino  animals  contain  latent  black,  but  transmit  it  appa- 
/  rently  to  only  about  half  of  their  offspring.  Matingsof  such  albinos  with 
I  red  or  yellow  animals  are  enumerated  in  Table  E. 

The  pigmented  young  produced  by  these  matings  are  41  black  pig- 
mented,  37  free  from  black  pigment  («.  e.,  bearing  only  red  or  yellow 
pigment  in  their  coats).  The  obvious  explanation  is  that  only  one  of 
the  two  gametes  which  united  to  form  each  of  these  albino  parents 
contained  latent  black,  the  other  being  free  from  it ;  consequently  only 
half  the  gametes  formed  by  the  albinos  contain  latent  black. 

TABLE  E. — Matings  of  albinos  {part  only  of  whose  gametes  transmit  latent  black) 
•with  red  or  yellow  animals.  Approximately  half  of  the  figmented  offspring 
have  black  pigment  in  their  coats. 


Voung 

red-white,  or  yellow  animal. 

Black- 
red. 

Black- 
yellow. 

Red. 

Yellow. 

Albino. 

Albino  cf  635  x  red-white  $  43... 
Albino  r?  635  X  red  9  47° 

3 

2 

... 

i 

... 

Albino  r?  635  X  red  Q  575  

Albino  r$  635  X  red  9  610 

2 

Albino  cf  635  X  red    $  610  and 
red  2  7<i 

c 

Albino  r?  635  x  red  2  755  

i 

Albino  (^  635  x  red  9  830  

2 

2 

i 

Albino  c?  635  X  red  9  1073.     . 
Albino  <J  635X  red-white  91093. 
Albino  r?  635  X  red  9  2008 

5 

i 
I 

Albino  r?  635  x  yellow  9  2001... 
Albino  9  815  X  yellow  $  2061.. 
Albino  9  i222  X  red  <?  2004  
Albino  9  "22  X  red  J*  2054  

Albino  9  i224Xyellow  <5"  1347.... 
Albino  J*   1516  x  red-white    9 
i  ^87 

i 

!  (agouti- 
red.) 

2 
I 

I 

2 
I 

i 
3 

i 

2 

... 

Total  

24 

6 

22 

8 

3 

3 

jo 

Parents  an  albino  and  a  red,  red- 

Young 

white,  or  yellow  animal  with 
recessive  albinism. 

Black- 
red. 

Black- 
yellow. 

Red. 

Yellow. 

Albino. 

Albino  c?  635  X  red-white  9  690  • 
Albino  tf  1516  x  red-white  9  1344- 
Albino  <£  I5i6xyellow  9  1346... 
Albino  cf  isi6xyellow  9  1348.... 
Albino  rf  1516  X  red-white  9  1434- 
Albino  y  1216  x  red  $  1386 

i 

2 

I 

2 
2 

i 

i 
i 

- 

i 

2 

I 

2 

Albino  9  i224Xred  cf  1386  
Albino  9  1236  x  red  rf*  1386  

I 
2 

... 

3 

i 

Total  

6 

V  V 

I 

I 

7 

COAT    CHARACTERS    IN    GUIXEA-PIGS    AND    RABBITS. 


39 


A  means  of  testing  the  validity  of  this  explanation  has  been  suggested 
by  Allen  (  :  04)  for  the  similar  case  of  chocolate  pigmentation  in  mice. 
If  the  albino  gametes  which  contributed  to  the  production  of  the  red  or 
yellow  offspring  in  the  matings  last  mentioned  were  really  free  from 
black,  then  two  of  these  hybrid  red  animals  (containing  recessive  albin- 
ism) when  mated  should  produce  albino  offspring  not  any  of  whose  gam- 
etes contain  latent  black.  Experiment  has  shown  this  to  be  the  actual 
result.  Albino  $  1999  was  produced  by  mating  two  hybrid  yellow 
animals  containing  recessive  albinism.  He  has  been  several  times 
mated  with  yellow  females  (see  Table  F)  and  has  produced  13  pig- 
mented  offspring,  all  yellow.  As  a  control  he  was  mated  also  with  a 
black  female  containing  recessive  albinism.  This  mating  produced 
3  albinos  and  i  black  pigmented  young.  Another  albino  tested, 
g  2059,  is  apparently  similar  in  nature  to  ^  1999,  for  when  mated 
with  red  9  610,  he  produced  3  young,  all  red  pigmented  (see  Table  F) . 
The  ancestry  of  this  albino  is  unknown  to  me,  as  I  obtained  him  from 
a  breeder,  and  as  no  other  test  of  this  sort  was  made  in  his  case,  the 
result  can  not  be  considered  conclusive,  because  of  the  small  number  of 
young  produced  ;  but  it  is  probable  that  all  his  gametes  were  free  from 
latent  black,  for  four  of  his  albino  daughters  by  albino  mothers  con- 
taining latent  black  form  albino  gametes  free  from  black,  as  well  as 
other  gametes  containing  black.  They  are  99  1216,  1222,  1224, 
and  1236,  Table  E.  Each  of  these  four  daughters  of  c?  2059,  all  that 
have  been  tested,  must  have  received  from  the  father  albinism  free 
from  latent  black,  for  the  mothers,  as  stated,  did  not  form  gametes 
containing  latent  black. 

TABLE  F. — Matings  of  albinos  (not  any  of -whose  gametes  transmit  latent  black) 
with  red  or  yellow  animals.     Not  any  of  the  offspring  are  black  pigmented. 


Parents. 

Young. 

Albino. 

Pure  red  or  yellow. 

Red. 

Yellow. 

Albino. 

Yellow  9  3105  
Yellow  9  32oo  .... 
Yellow  Q  3085  
Red  9  610 

3 

3 

3 
5 

... 

Total           

3 

ii 

Albino. 

Yellow  (albinism 
recessive). 

Red. 

Yellow. 

Albino. 

O    174.6 

2 

3 

2 
I 

9  1348 

9  9  2063  and  3°36- 

... 

Total 

2 

6 

40  COAT    CHARACTERS    IN    GUINEA-PIGS    AND    KABBITS. 

Although  the  discovery  of  the  differences  among  albinos,  as  regards 
matings  with  red  animals,  was  made  by  mere  accident  while  comparing 
the  matings  of  ef  635  with  those  of  other  albino  males,  I  have  since 
found  it  possible  to  produce  at  will  albinos  free  from  latent  black  (like 
cf  1999)  by  beginning  with  matings  between  ordinary  albinos  (all  of 
whose  gametes  transmit  latent  black)  and  red  or  yellow  animals.  The 
following  case  illustrates  the  method  used  :  Albino  cf  2002  is  shown  by 
matings  recorded  in  Table  D  to  form  only  gametes  transmitting  latent 
black.  For  by  red  or  yellow  females  he  has  produced  to  pigmented 
young,  all  with  more  or  less  black  in  their  coats.  From  the  mating 
with  yellow  9  2001  there  resulted  3  black-yellow  young,  9  9  2033- 
2035.  Each  of  these,  according  to  the  hypothesis  offered,  received 
from  one  parent  albinism  with  latent  black,  and  from  the  other  yellow 
free  from  black.  In  forming  gametes  the  yellow-black  hybrids  should 
produce  gametes  of  four  different  kinds,  all  equally  numerous  (on  the 
hypothesis  that  albinism  is  inherited  independently  of  specific  pigments, 

alb.  o  20°2         x  yel.  ?  Z001 

bL-yel   °°  2033-3035  yel.  O  2061 


yet.  $1346   yel.^1347   yel.  $1348     yel.  °.  1349    yel.?  1350  yel.-wh.$  1351  3bl.-yel.youn$ 
(alb.  recessive)    (pure)      (alb.  recessive)     (pure)  (pure)     (alb.  recessive) 

FIG.  jo.—  A  genealogical  table  ;  for  description,  see  text. 

as  previously  explained,  viz,  (i)  yellow,  (2)  black,  (3)  albinism  [yellow 
latent],  (4)  albinism  [black  latent].  Accordingly,  when  a  mating 
of  such  a  hybrid  is  made  with  a  pure  yellow  animal,  such  as  cf  2061 
(see  fig.  10),  gametic  unions  of  four  different  sorts  should  occur  with 
equal  frequency,  viz,  (i)  yellow  -f  yellow,  producing  pure  yellow 
young  ;  (2)  black  -f-  yellow,  producing  black-yellow  young  free  from 
recessive  albinism  ;  (3)  albinism  [yellow  latent]  +  yellow,  producing 
yellow  young  (with  albinism  recessive)  ;  (4)  albinism  [black  latent]  + 
yellow,  producing  black-yellow  young  (with  albinism  recessive).  That 
is,  half  the  young  should  be  yellow,  half  should  be  black-yellow  ;  and 
of  each  sort  half  again  should  contain  recessive  albinism,  half  should  be 
free  from  it.  In  the  case  under  discussion  (see  diagram,  fig.  10)  there 
were  produced  6  yellow  and  3  black-yellow  young,  but  in  a  series  of 
matings  equality  of  the  two  classes  would  undoubtedly  have  been  more 
closely  approximated,  as  Table  E  indicates.  The  yellow  young  alone 
were  tested  for  the  presence  of  recessive  albinism,  and  it  was  found  in 
exactly  half  of  them,  viz,  9  9  1346,  1348,  and  1351,  the  test  indicating 
that  the  other  three  yellow  young  are  pure.  The  method  by  which 


COAT    CHARACTERS    IN    GUINEA-PIGS    AND    RABBITS. 


albinos  free  from  latent  black  may  be  obtained  from  red  or  yellow 
hybrids,  like  9?  *346,  1348,  and  1351,  has  already  been  explained. 
It  is  simply  to  mate  the  hybrids  inter  se,  when  there  should  be  produced 
albino  young,  approximately  one-fourth  of  all  the  young  produced,  and 
these  albinos  should  be  free  from  latent  black.  A  number  of  albinos 
have  been  so  produced  in  these  experiments,  but  only  one  of  them,  viz, 
c?  1999,  Table  F,  has  yet  been  tested.  It  is  evident  that  his  gametes 
are,  as  expected,  free  from  latent  black. 

This  experiment  indicates  methods  of  practical  utility  to  the  breeder 
who  desires  either  albinos  as  free  as  possible  from  peripheral  pigment 

TABLE  G. — Matings  inter  se  of  red  or  yellow  animals  having  albinism  recessive. 
None  of  the  young-  black-pigmented.     Expected  proportion   of  albinos  i  in  4. 


Young. 

Parents. 

Red  or 
red-white. 

Yellow 
or  yellow- 
white. 

Albino. 

Yellow  $  1147  x  yellow  9  ^32  

Yellow  $  1*47  X  yellow  9  1487  

Yellow^  1147  x  vellow  9  1786  

2 

T 

Red  $  1433  X  red  9  ^43  

7 

Red  (^  1453  x  red  9  1291  

2 

2 

Red  (^  1453  X  red  9  I297  

2 

J 

Red  $  1453  X  red  9  ?  

Red  (^  1477  X  red  9  1292  

I 

Yellow  (^  I998X  yellow  $  9  I35I  an^  I535-- 

4 

2 

Total 

28 

18 

g 

4 

5 

or  animals  of  various  shades  of  red  or  yellow.  For  (i)  albinos  free 
from  latent  black  have  much  less  peripheral  (chocolate  or  chocolate 
and  black)  skin  pigment  than  others,  and  (2),  when  mated  with  red 
or  yellow  animals  they  frequently  produce  young  of  a  lighter  shade  of 
red  or  yellow  than  that  of  the  pigmented  parent.  He  who  mates 
ordinary  albinos  with  red  animals  in  hope  of  obtaining  yellows  will 
be  sorely  disappointed,  for  the  young  will  be  mottled  with  black 
(received  latent  from  the  albino  parent) ;  but  he  who  employs  albinos, 
such  as  I  have  described,  in  matings  with  red  or  yellow  animals,  may 
doubtless  with  patience  realize  his  fondest  hopes.  By  this  method  I 
have  been  able  to  produce  cream-colored  animals  of  a  much  lighter 
shade  than  any  I  ever  saw  before.  Theoretically  it  should  be  possible 
by  following  up  this  method  to  produce  animals  practically  white,  but 


COAT    CHARACTERS    IN   GUINEA-PIGS    AND    RABBITS. 


with  dark  eyes.  Time  will  show  whether  this  is  possible.  It  is  not 
improbable  that  practical  difficulties  may  be  encountered.  Experi- 
enced breeders  say  that  the  "  purest"  albino  guinea-pigs  (/.  e.,  those 
most  free  from  peripheral  pigmentation)  incline  to  sterility.  Two 
cases  which  have  occurred  in  my  own  experiments  make  me  think 
there  is  some  truth  in  this  idea.  Further,  albinos  free  from  latent 
black  have  not  yet  been  mated  inter  se,  but  I  shall  not  be  surprised 

TABLE  H. — Mat ittgs  of  males  mentioned  in  Table  G  -with  animals  black  pig- 
menttd,  but  having  albinism  recessive.  The  expected  proportion  of  albinos 
is  i  in  4. 


Young. 

Parents. 

Black- 
red. 

Black- 
yellow. 

Yellow. 

Agouti- 
yellow. 

Albino. 

Red  /-?  IOIQ  x  agouti  9  2020.... 

2 

Yellow  $  1147  X  black-yellow 

91  IAQ 

Yellow  $  1147  X  silver  agouti- 
yellow  9  1252       

I 

2 

Yellow  (^   1147   X  black-yellow 
$20-14. 

i 

i 

Total              

2 

2 

2 

7 

TABLK  I. — Matings  of  males  mentioned  in  Table  G  -with  albino  females,     ft  is 
expected  that  half  the  offspring  -will  be  albinos. 


Parents. 

Young. 

Black- 
red. 

Black- 
yellow. 

Agouti- 
red. 

Albino. 

2 

4 
i 

4 

2 

2 

2 

3 

Yellow  (^  1  147  X  albino  9  "  Himalayan  " 

Yellow  r?  1147  x  albino  9  815  

Red  ^  I433X  albino  9  *544  

2 

ToUl  

^_  4 

3 

-•  —  —  -V1       —  ' 

9 

2 

13 

to  find  them  relatively  unproductive  when  this  is  done,  for  the  hybrids 
bred  inter  sc  have  in  certain  cases  produced  fewer  albino  young  than 
they  should  produce  on  the  Mendelian  hypothesis.  Thus,  an  exami- 
nation of  Table  G  shows  that  only  8  albinos  have  been  produced  in  a 
total  of  54  young,  where  13.5  are  expected.  Nevertheless,  this  may 
be  only  a  chance  deviation  from  the  expected  proportion  of  albinos 
which  will  disappear  as  larger  numbers  are  produced.  Tables  H  and 
I  indicate  that  the  hybrid  males  employed  in  the  matings  enumerated 


COAT    CHARACTERS    IN    GUINEA-PIGS    AND    RABBITS.  43 

in  Table  G  really  produce  a  full  quota  of  albino  gametes,  and  that 
these  are  entirely  fertile  when  they  meet  gametes  transmitting  black, 
either  active  or  latent.* 

It  is  a  question  of  much  interest,  theoretical  as  well  as  practical, 
whether  animals  of  a  particular  type,  when  produced  by  cross-breed- 
ing, form  the  same  sort  of  gametes  as  are  produced  by  pure-bred 
animals  of  the  same  type.  In  the  case  of  albinos  this  evidently  is  not 
always  true.  From  an  albino  which  forms  gametes  all  of  which  trans- 
mit latent  black,  there  may  be  produced,  as  we  have  seen,  by  cross- 
breeding with  a  red  animal  and  then  interbreeding  the  hybrids,  albinos 
of  three  different  sorts  as  regards  the  transmission  of  latent  black 
pigment.  Again,  the  character  of  a  red  race  which  breeds  true  may 
be  modified  by  cross-breeding  with  black,  resulting  in  the  production  of 
yellow  young.  Thus  two  red  animals,  young  of  black  (red  recessive) 
red&?  red?  2007 


redo  2004       red  ? 2026     bl.?  2013  red  £  2054     red  £  ?      red  $  2007 


I  I 

red?  1307  bl.(red  recessive)  5  1180 


red   ?  309S  red  £   3082 

( 
3  yellow  young 

FIG.  ii.  —  A  genealogical  table  showing  how  cross-breeding  between  red  and  black  may  cause  variation 
in  the  intensity  of  the  red. 

tf  1180,  by  two  different  pure-bred  red  females,  when  mated  together, 
produced  a  litter  of  3  yellow  young.  The  relationships  involved  will 
perhaps  be  more  readily  understood  from  the  above  diagram  (fig.  n). 
Apparently  the  cross  with  black  induced  variation  in  the  intensity  of 
the  pigmentation  transmitted  by  the  gametes  bearing  red,  so  that  some 
of  the  zygotes  which  were  formed  bore  the  dilute  form  of  red,  viz, 
yellow. 

BLACK-EYED   WHITE. 

Guinea-pigs  of  this  sort  have  hair  and  skin  very  free  from  pigment, 
indeed  in  the  integument  of  the  living  animal  I  can  detect  no  pigment 
at  all,  yet  the  eyes  are  black  pigmented.  Two  animals  of  this  sort 
have  been  born  in  the  course  of  my  experiments,  and  I  have  likewise 
experimented  with  two  others  obtained  by  purchase.  They  are  not 
albinos  and  do  not  contain  recessive  albinism,  at  least  those  which  I 
have  had  do  not.  They  are  of  spotted  parentage  and  may  be  considered 
spotted  animals  in  which  the  typical  pigment  patches  show  an  extreme 


*  Experiments  made  since  the  foregoing  was  written  show  that  albinos  free 
from  latent  black  are  entirely  fertile  inter  se.  Further,  the  deficiency  of  albinos 
observed  at  first  is  now  disappearing. 


44  COAT    CHARACTERS    IN    GUINKA-PIGS    AND    RABBITS. 

condition  of  reduction.  The  successive  steps  by  which  the  pigmenta- 
tion of  guinea-pigs  undergoes  reduction  are  about  as  follows:  (i)  The 
pigment  centers  are  all  functional,  but  the  pigment  areas  do  not  quite 
meet  along  the  middle  of  the  ventral  surface,  or  in  the  forehead.  Per- 
haps the  pigment  fails  to  reach  one  or  more  of  the  feet  also.  (2)  One 
or  both  shoulder  patches  are  wanting,  producing  the  Dutch-marked 
type  (compare  fig.  6,  p.  12).  (3)  The  side  patches  are  also  wanting;  only 
the  rump  and  sides  of  the  head  are  pigmented  (fig.  2,  p.  10).  (4)  The 
rump  patch  disappears ;  only  the  sides  of  the  head  are  pigmented,  and 
here  the  patches  are  small,  or  one  or  more  of  them  may  be  wanting 
(fig.  4,  p.  n).  An  extreme  condition  of  this  sort  is  represented  by 
c?  721 ,  whose  coat  was  entirely  unpigmented  except  for  a  small  patch  of 
black  about  5  mm.  square  on  the  outer  surface  of  his  right  ear.  (5) 
The  skin  is  wholly  unpigmented,  though  the  eyes  are  as  in  all  the  fore- 
going stages  dark.  One  can  by  selection  progress  in  either  direction 
through  this  series  of  changes,  either  increasing  or  decreasing  the 
number  and  extent  of  the  pigment  patches,  but  it  is  impossible  without 
long-continued  selection  to  fix  the  color  pattern  at  any  particular  stage  in 
the  series  ;  perhaps  it  is  wholly  impossible  to  do  so,  as  Cu6not  ( :  04,  p.  LV) 
asserts  on  the  basis  of  his  studies  on  mice,  but  this  I  very  much  doubt. 
I  doubt  it  first,  because  we  do  find  color  patterns  of  this  sort  firmly  fixed 
in  many  wild  species,  such  as  antelopes,  skunks,  etc. ;  secondly,  and  still 
more,  I  doubt  it  because  of  what  we  see  accomplished  in  domesticated 
animals.  Take  the  case  of  cattle  alone.  Different  breeds  of  cattle  have 
often  distinctive  color  patterns,  as  well  as  specific  pigments  in  their 
coats.  Holstein  cattle  are  white,  marked  with  large  but  more  or  less 
irregular  black  spots,  the  color  pattern  being  apparently  not  definitely 
fixed.  Dutch  belted  cattle,  probably  derived  from  the  same  general 
source  as  the  Holstein,  have  for  a  long  time  been  subjected  to  a  rigid 
selection  for  a  more  definite  color  pattern,  viz,  an  animal  wholly  black 
except  for  a  broad  white  belt  around  the  middle  of  the  body.  To  this 
type  the  breed  is  said  to  keep  very  true. 

Pure-bred  Hereford  cattle  as  kept  at  the  present  time  in  America 
are  red  over  the  greater  part  of  the  body,  but  are  invariably  white- 
faced  ;  a  longitudinal  white  stripe  extends  down  the  middle  of  the 
back,  and  the  belly  and  flanks  are  more  or  less  extensively  marked 
with  white.  The  white  face,  though  now  rigidly  insisted  upon  and 
always  seen  in  pure-bred  herds,  has  not  always  been  so  common  in  the 
breed.  A  half  century  or  more  ago,  according  to  Shaw  (  :  03),  rival 
breeders  advocated  white-faced  and  mottled-faced  Herefords,  but  the 
former  prevailed,  and  by  continued  selection  the  mottled-faced  con- 
dition has  now  apparently  been  eliminated  from  the  breed. 

These  cases  indicate  that  certain  of  the  typical  color  patches,  as,  for 
example,  the  cheek  patches  of  cattle,  can  by  continued  selection  be 


COAT    CHARACTERS    IN    GUINEA-PIGS    AND    RABBITS.  45 

eliminated  altogether,  while  others  are  kept  at  their  maximum  inten- 
sity. How  this  is  possible  we  could  understand  better  if  we  knew  in 
what  condition  pigment  characters  are  transmitted  in  the  germ.  From 
the  experimental  evidence  alone  it  would  seem  probable  that  the  dif- 
ferent color  patches  are  represented  in  the  germ  by  different  elements 
separately  heritable,  possibly  in  different  chromosomes — though  of  this 
we  know  absolutely  nothing — and  that  as  a  result  of  long  selection 
these  separately  heritable  elements  may  become  firmly  associated  with 
particular  body  regions.  From  the  mode  of  development  of  the  hair 
pigments  as  described  by  Leo  Loeb  ('97)  and  confirmed  by  observa- 
tions of  Mr.  Howard  and  myself,  it  is  clear  that  the  pigments  are 
formed  in  the  Malpighian  layer  of  the  epidermis.  A  pigment  patch, 
then,  is,  morphologically,  simply  the  pigmented  epidermis  of  a  particular 
body  region,  and  its  character  is  determined  by  whatever  determines  the 
character  of  the  epidermis  in  that  body  region. 

That  black-eyed  white  animals  are  essentially  animals  of  the  centrip- 
etally  pigmented  type  is  shown  by  breeding  them  inter  se  or  by  mat- 
ing them  with  albinos.  In  every  case  thus  far  I  have  obtained  only 
young  with  one  to  several,  or  even  with  a//,  of  the  typical  pigment 
patches.  The  task  of  establishing  a  black-eyed  white  race  which  will 
breed  true  is  similar  to  that  of  establishing  a  Dutch-marked  race  which 
will  breed  true,  or  in  cattle  a  white-faced  race  like  the  Hereford.  It 
is  not  to  be  accomplished  in  a  single  generation,  but  I  doubt  not  its 
possibility.  When  guinea-pigs  have  been  bred  to  a  particular  color 
pattern  for  many  generations,  we  can  form  a  better  estimate  of  the 
magnitude  of  the  task  involved,  and  possibly  meantime  may  learn 
something1  about  the  mechanism  of  transmission  of  the  color  patches. 

The  specific  pigments  transmitted  by  black-eyed  white  animals  are 
probably  determined  by  the  same  rules  that  govern  in  the  latent  pig- 
mentation of  albinos.  These  pigments  probably  differ  according  to  the 
parentage  in  different  cases,  or  more  correctly  according  to  the  latent 
pigmentation  which  each  individual  received  from  its  parents.  Indeed, 
it  is  not  impossible  that  vanished  pigment  patches  are  merely  latent 
pigment  patches,  and  that  the  reason  why  these  keep  reappearing  in 
such  a  seemingly  erratic  fashion  is  that  they  keep  emerging  from 
latency  under  the  influence  of  cross-breeding.  In  the  black-eyed  white 
animals  with  which  I  have  experimented,  red  as  well  as  black  spots 
are  apparently  transmitted  in  the  gametes  formed,  but  I  should  expect 
that  in  animals  different  in  origin  red  might  be  transmitted  apart  from 
black  or  vice  versa. 

I  have  not  examined  with  the  microscope  the  eye-pigments  of  the 
different  self-colored  varieties  of  the  guinea-pig.  From  a  superficial 
examination,  however,  I  should  say  that  black  pigment  is  present  in 


46  COAT   CHARACTERS    IN   GUINEA-PIGS   AND   RABBITS. 

every  case  except  that  of  the  albino.  Yet  we  have  seen  that  red  and 
yellow  animals,  which  have  no  black  pigment  in  their  coats,  do  not 
transmit  black  coat-pigment  to  their  offspring,  though  they  do  transmit 
black  eye-pigment.  We  might  conclude  that  eye-pigment  is  something 
altogether  different  from  and  independent  of  coat-pigment,  but  two 
considerations  negative  this  idea  :  (i)  Black-eyed  white  animals  mated 
with  albinos  produce  animals  with  coat-pigment  in  the  typical  patches, 
a  thing  which  neither  parent  possessed  ;  (2)  in  mice,  animals  with  coat 
patches  but  devoid  of  eye-pigment,  when  mated  with  unrelated  albinos, 
produce  offspring  with  pigmented  eyes,  again  a  character  which  neither 
parent  possessed  (Darbishire,  104).  From  these  facts  we  see  that  a  cer- 
tain connection  does  exist  between  eye-pigmentation  and  coat-pigmenta- 
tion, though  apparently  it  is  less  close  than  that  between  one  coat-patch 
and  another  coat-patch.  The  disappearance  of  eye-pigmentation,  like 
the  disappearance  of  coat- pigmentation,  is  probably  due,  in  the  case  of 
ordinary  albinos,  to  latency  in  the  germ  of  a  particular  hereditary  unit. 
This  condition  of  latency,  it  is  evident,  can  be  made  to  disappear  by 
cross-breeding  with  any  animal  of  the  centripetally  pigmented  type. 
But  in  centripetally  pigmented  animals,  as  we  shall  see,  disappearance 
of  eye-pigment,  when  once  it  has  occurred,  is  apparently  beyond  recall, 
at  least  by  cross-breeding  with  albinos.  This  is  indicated  by  the  instruc- 
tive experiments  of  Darbishire  ( :  04),  which  we  shall  presently  examine 
more  in  detail. 

A  condition  which  might  be  described  as  semi-latency  of  a  coat- 
•  pigment  was  observed  in  the  case  of  a  red-white  animal,  9  915,  which 
\  was  mated  with  red  cf  1019.  To  my  great  surprise  she  produced  in 
two  successive  litters  four  young  having  black-reft  coats.  This  was 
contrary  to  any  previous  experience  (compare  Table  G),  and  I  at  once 
sought  for  an  explanation.  Upon  looking  the  animal  over  carefully 
I  found,  what  I  had  before  overlooked,  that  she  had  a  sacral  patch  of 
black  skin,  though  not  a  single  hair  of  her  body,  so  far  as  I  could  dis- 
cover, was  black  pigmented.  The  capacity  to  form  black  integumen- 
tary pigment  was  evidently  present  in  the  animal,  though  its  influence 
extended  only  to  the  epidermis  proper,  not  to  the  hair-follicles.  One 
often  sees  in  dogs,  for  example  in  fox-terriers,  black  skin  spots  of  this 
sort  in  body  regions  where  the  coat  is  entirely  white.  The  character 
semi-latent  in  9  915  came  into  full  activity  in  four  of  her  offspring 
by  a  male  devoid  of  that  character. 

Black  skin  is  not  infrequently  seen  on  the  feet  of  red  guinea-pigs, 
but  such  animals  do  not  produce  young  with  black  hairs  when  they 
are  mated  with  other  red  animals.  A  comparison  of  this  result  with 
that  described  in  the  case  of  9  915  serves  to  emphasize  the  distinction 
which  has  been  made  between  centrifugal  and  centripetal  pigmentation 


COAT    CHARACTERS    IN    GUINEA-PIGS    AND    RABBITS.  47 

(see  p.  9).  The  black-footed  guinea-pig  has  the  former,  which  it 
transmits  to  its  offspring  ;  it  does  not  possess  the  latter  and  its  offspring 
never  do,  unless  a  mating  has  been  made  with  an  animal  having  pig- 
mentation of  that  sort.  The  black-footed  red  guinea-pig,  as  regards 
black  pigmentation,  is  in  exactly  the  same  condition  as  an  albino  with 
clark-pigmented  extremities  ;  centripetal  black  pigmentation  is  fully 
latent  in  it. 

Black-eyed  white  animals,  of  the  sort  which  I  have  had,  and  ani- 
mals like  £  9I5»  are  centripetallv  pigmented  animals  in  which  the 
capacity  to  form  black  pigment  in  the  typical  central  patches  is  semi- 
latent,  /.  <?.,  they  may  apparently  transmit  the  character  in  a  fully  active 
condition,  when  mated  inter  se,  across  with  animals  having  a  different 
type  of  pigmentation  being  unnecessary  for  this  purpose. 

Darbishire's  pink-eyed  but  centripetally  pigmented  mice,  if  they 
possessed  at  all  the  capacity  to  form  eye-pigment,  must  have  possessed 
it  in  a  more  than  latent  condition,  for  they  bred  true  inter  se,  and  though 
a  cross  with  albinos  brought  the  character  into  full  activity,  there  are 
strong  reasons  for  believing,  as  we  shall  presently  see,  that  the  capacity 
to  form  eye-pigment  was  recovered,  not  from  the  pink-eyed  animal, 
but  from  the  albino  with  which  it  was  mated.  It  is  to  be  expected 
that  continued  selection  and  inbreeding  of  black-eyed  white  guinea- 
pigs  would  establish  a  condition  of  the  coat-pigment  patches  similar 
to  that  of  the  character  eye-pigmentation  in  Darbishire's  pink-eyed 
mice,  a  condition  which  goes  beyond  the  latency  of  centripetal  pig- 
mentation in  albinos,  and  may,  for  all  we  at  present  know,  amount  to 
elimination  of  the  character  in  question  from  the  germ.  This  question 
offers  an  attractive  field  for  further  investigation. 

Comparison  'with  pink-eyed  mice. — The  dark-eyed  mice  obtained 
by  Darbishire  (  :  04)  upon  mating  pink-eyed  spotted  mice  with  albinos, 
yielded  an  interesting  result  when  bred  inter  se.  Approximately  one- 
fourth  of  the  young  were,  as  we  should  expect,  albinos  ;  one-half  were 
dark-eyed,  like  their  parents,  the  primary  hybrids ;  and  one-fourth 
were  pink-eyed  and  spotted.  We  should  naturally  expect  the  dark-eyed 
young  (like  their  parents)  to  contain  recessive  albinism,  and  the  pink- 
eyed  spotted  ones  to  be  free  from  it,  like  their  pink-eyed  grandparents. 
While  in  many  cases  this  was  undoubtedly  true,  in  others  it  was  not 
true  ;  for  Darbishire's  breeding  experiments  show  that  some  of  the 
dark-eyed  animals  did  not  contain  recessive  albinism,  and  that  some  of 
the  pink-eyed  ones  did.  Further,  the  "extracted"  albino  young  in 
some  cases  behaved  differently  from  their  albino  grandparents  in 
crosses  with  pink-eyed  spotted  animals.  They  produced  pink-eyed 
as  well  as  dark-eyed  hybrids,  the  two  sorts  being  approximately  equal 
in  number  (7  pink-eyed  to  6  dark-eyed,  Darbishire,  :  04,  Table  D,  p.  24). 


48  COAT   CHARACTERS    IN   GUINEA-PIGS   AND    RABBITS. 

From  this  it  is  clear  that  the  five  albino  parents  which  gave  the  result 
just  described  transmitted  in  approximately  half  their  gametes  the 
pink-eyed  and  in  half  the  dark-eyed  condition.  These  albinos  are  com- 
parable in  the  matter  of  the  pink-eyed  character  with  my  albino  guinea- 
pigs  of  Table  E  in  the  matter  of  black  coat-pigment.  A  close  parallel 
exists  throughout  the  two  cases.  Darbishire's  original  albinos  all  con- 
tained latent  the  character  pigmented  eye.  This  character  was  invaria- 
bly brought  into  activity  by  across  with  the centripetally  pigmented  but 
pink-eyed  race.  That  race  would  seem  not  to  have  possessed  the 
character  eye-pigmentation,  even  in  a  state  of  latency  which  a  cross 
with  albinos  would  bring  into  activity  ;  for  half  the  gametes  formed 
by  the  hybrids  apparently  lacked  the  character  eye-pigmentation,  and 
that  character  was  as  often  associated  latent  with  the  albino  character, 
as  it  was  associated  active  with  the  alternative  character,  standing  for 
centripetal  pigmentation.  If  so,  the  hybrids  must  have  formed  with 
equal  frequency  gametes  of  these  four  sorts:  (i)  pigmented  coat, 
pink-eye,*  (2)  pigmented  coat,  dark-eye,  (3)  albinism  [pigmented  coat 
and  pink-eye  latent],  (4)  albinism  [pigmented  coat  and  dark-eye  latent]. 

Hybrids  forming  sets  of  gametes  like  these,  when  mated  inter  sc, 
should  produce  young  visibly  of  three  classes  in  the  proportions,  9 
dark-eyed  pigmented  to  3  pink-eyed  pigmented  to  4  albino.  The  num- 
bers observed  by  Darbishire  are  287  (or  284?)  dark-eyed  pigmented, 
131  (or  134?)  pink-eyed  pigmented,  and  137  albino  young. 

On  the  hypothesis  which  I  have  suggested,  these  young,  though 
visibly  of  only  three  different  sorts,  should  really  fall  into  nine  classes, 
whose  numerical  proportions  are  theoretically  as  follows  :f 


Class  (5), 
Class  (\),^Pd(Ap)  "I  Class  (6) , 


Class  (2),  2  Pd(p)        i    9  pigmented 
Class  (3),  2  Pd(A  <t)   f     dark-eyed.          Class  (7), 
Class  (4),  i  Pd  Class  (8), 

Class  (9), 


PP  (A  P)\  3  pigmented 
Pp  >      pink-eyed. 

A  [.dp]       ) 

A[dd~\       ^  4  albinos. 

Alt  A      ) 


This  classification  rests  on  the  assumption  that  eye-pigmentation  may 
be  inherited  apart  from  coat-pigmentation,  /.  £.,  that  the  primary 
hybrids  are  really  ^/-hybrids  in  the  Mendelian  sense.  It  involves  the 
further  hypothesis  that  eye-pigmentation  was  invariably  latent  in  the 
original  albino  stock  used,  and  as  invariably  absent  from  the  pink-eyed 

*  Although  the  pink  eye  is  due  merely  to  absence  of  pigment  from  the  eye, 
just  as  albinism  to  absence  of  pigment  from  the  eye  and  coat,  it  is  convenient 
in  both  cases  to  speak  of  the  negative  character  as  if  it  were  positive.     This  can 
be  done,  I  trust,  without  confusion  to  the  reader. 

*  EXPLANATION.— A  =  albino;    P  =  pigmented;   d  =  dark-eyed;  /  =  pink- 
eyed;   (    )  indicate  recessive  characters,  [    ]  latent  characters.     The  relative 
frequency  of  occurrence  of  individuals  of  each  class  is  indicated  by  a  coefficient. 


COAT    CHARACTERS    IN   GUINEA-PIGS    AND    RABBITS. 


49 


pigmented  animals  (at  least  in  a  state  capable  of  becoming  active  as  a 
result  of  matings  with  albinos). 

Let  us  now  inquire  whether  Darbishire's  experiments  indicate  the 
existence  of  these  various  hypothetical  classes  or  not.  Darbishire  gives 
in  the  first  part  of  his  Table  E,  page  35,  the  results  of  mating  inter  se 
dark-eyed  pigmented  animals  of  generation  F2.*  On  the  "ancestry" 
hypothesis  these  should  all  breed  much  alike,  for  their  ancestry  is  sim- 
ilar in  all  cases ;  on  the  hypothesis  which  I  have  stated,  they  include 
the  four  distinct  sorts  of  individuals  which  I  have  called  classes  (i)  to 
(4),  page  48,  and  these  will  breed  very  differently  one  from  another. 
An  examination  of  Darbishire's  table  shows  that  in  fact  the  various 
pairs  of  pigmented  dark-eyed  animals  gave  results  of  four  different  sorts. 

I.  The  following  pairs  gave  young  of  three  sorts — dark-eyed,  pink- 
eyed,  and  albino  : 


ifoung 

Pd. 

Pp. 

A. 

2H  48   

2 

2 

2H  <;2 

•j 

i 

I 

2H  Q-?  .  . 

2 

2 

I 

Total  

4 

On  the  Mendelian  hypothesis  each  of  the  parents  in  these  three  fami- 
lies must  have  furnished  gametes  bearing  the  pink-eyed  character  as 
well  as  gametes  bearing  the  albino  character.  If  so,  and  if  each  of  these 
characters  was  represented  in  half  the  gametes  formed,  and  the  two 
characters  were  independent  of  each  other,  then  the  parents  were  of 
class  ( i) ,  page  48,  and  the  young  should  be  as  9  P  d  to  3  P p  to  4  A, 
which  approximates  roughly  the  observed  7  to  4  to  4. 

II.  The  following  pairs  gave  only  dark-eyed  and  pink-eyed  young, 
without  albinos : 


Pair. 

Young. 

Pd. 

Pp. 

2H  390  

5 
4 
4 

I 

2 
I 
I 

I 
2 

2H  70/9 

2H  ci/3 

2H   I7Q. 

2H  142  

Total  

23 

7 

*  I  adopt  here  and  in  the  following  pages  Bateson's  convenient  notation  for 
the  successive  "  filial  "  generations  following  a  cross,  viz,  Ft,  F8,  F8,etc. 


COAT    CHARACTERS    IN    GUINEA-PIGS    AND    RABBITS. 


A  result  of  this  sort  can  have  followed  either  from  matings  inter  se 
of  animals  of  class  (2),  page  48,  or  from  matings  of  such  animals  with 
those  of  class  (i).  In  either  case  the  young  should  be  353  Pdto  i  Pp, 
a  ratio  closely  approximated  in  the  observed  23  P  d  to  7  Pp. 

III.  The  following  pairs  gave  only  dark-eyed  and  albino  young, 
without  pink-eyed  pigmented  ones  : 


Pair. 

Young. 

Pd. 

A. 

2H  y>a.        

4 
4 
7 
6 
3 

i 

i 
i 

2 

zH  ejoS 

2H  96 

2H  QQ 

Total 

24 

6 

Such  a  result  would  be  produced  either  by  mating  inter  se  individ- 
uals of  class  (3),  page  48,  or  by  mating  individuals  of  that  class  with 
those  of  class  (i).  In  either  case  the  young  should  be  as  3  Pdto  i  A. 
The  observed  numbers,  2410  6,  are  not  greatly  at  variance  with  this  ratio, 
considering  the  small  number  of  young  produced. 

IV.  The  following  pairs  produced  only  dark-eyed  pigmented  young, 
without  either  albinos  or  pink-eyed  pigmented  young ; 


Pair. 

Young. 
Pd 

21136  

•7 

aH  40  .  . 

I 

2H5i  

aHgz  

•3 

Total  

17 

Such  a  result  should  follow  mating  inter  se  two  individuals  of  class 
(4),  page  48,  or  mating  an  individual  of  that  class  with  one  from  any 
of  the  other  three  classes,  (i)  to  (3),  or  from  a  mating  between  classes 
(2)  and  (3). 

Accordingly,  in  the  eighteen  pairs  which  Darbishire  formed  of  dark- 
eyed  pigmented  mice  of  this  second  filial  generation  (omitting  only 
one  pair  which  gave  but  a  single  young),  we  get  evidence  of  the 
probable  existence  of  all  four  of  the  hypothetical  classes  of  dark-eyed 
individuals.  If  the  pairs  were  taken  quite  at  random  without  regard 
to  the  recessive  characters  present  in  the  different  animals  (and  this 
was  evidently  the  case,  since  Darbishire  does  not  admit  the  existence 


COAT    CHARACTERS    IN   GUINEA-PIGS    AND    RABBITS. 


of  such  characters) ,  we  should  expect  from  the  theoretical  numerical 
frequencies  of  classes  (i)  to  (4)  that  pairs  giving  the  four  sorts  of  results 
described  would  be  as  follows.  The  observed  frequencies  are  for  con- 
venience in  comparison  given  in  a  parallel  column. 


Group. 

Expected 
frequency. 

Approxi- 
mately. 

Observed 

frequency. 

I  

28 

•> 

II  

-?8 

Ill  

38 

IV  

c-> 

J 

The  agreement  between  expected  and  observed  frequencies,  it  will 
be  noticed,  is  as  close  as  could  reasonably  be  expected  in  so  small  a 
number  of  pairs. 

Again,  Darbishire  mated  dark-eyed  animals,  like  those  whose  mat- 
ings  we  have  been  discussing,  with  dark-eyed  animals  of  different 
parentage,  one  of  the  parents  having  been  a  hybrid,  the  other  an  albino. 
In  all  such  cases  the  albino  parent  evidently  possessed  and  transmit- 
ted to  its  offspring  the  dark-eyed  character,  for  none  of  the  pigmemted 
young  were  pink-eyed.  But  the  hybrid  parent,  according  to  our  hypoth- 
esis, transmitted  the  pink-eyed  character  to  half  its  offspring,  forming 
gametes  as  follows  (see  p.  48)  :  P d  +  Pp  +  A  \_d]  +  A  [>]. 

Union  of  the  gametes  of  the  albino  parent,  all  A  [«T] ,  with  gametes 
like  these  would  produce  young  as  follows  : 

Pd(Ad)  +  Pd  (Ap)  +  A  [dd]  +  A  [_dp~\. 

But  as  Darbishire  utilized  in  the  experiment  under  discussion  only 
pigmented  animals,  we  are  concerned  at  present  only  with  the  first  two 
classes  of  young.  They  are  identical  in  character  with  individuals  of 
classes  (3)  and  (i),  respectively  (p.  48),  but  occur  in  equal  numbers, 
whereas  in  a  group  of  hybrids  like  that  described  on  page  48,  class 
(i)  is  twice  as  abundant  as  class  (3). 

The  question  now  before  us  is,  if  individuals  of  classes  (i)  and 
(3)  be  taken  with  equal  frequency  to  mate  with  individuals  taken  at 
random  from  a  mixture  of  classes  (i)  to  (4)  in  the  proportions  indi- 
cated on  page  48,  what  sorts  of  offspring  are  to  be  expected  and  in  what 
proportions  in  the  various  pairs  formed.  Making  the  calculations  by 
the  methods  already  explained,  we  find  that  pairs  should  occur  giving 
the  same  four  sorts  of  results  as  in  the  previous  case  (pp.  49  and  50, 1 
to  IV) ;  but  these  pairs  should  occur  in  frequencies  somewhat  different. 


5- 


COAT   CHARACTERS   IN   GUINEA-PIGS   AND    RABBITS. 


The  pairs  recorded  by  Darbishire  (p.  35,  Table  E,  middle  section) 
which  fall  into  these  respective  groups  are  as  follows  (omitting  only 
one  pair  which  produced  3  albinos  and  which  might  fall  into  either 
Group  I  or  Group  III)  : 


GROUP  I. 

GROUP  II. 

Pair. 

Young. 

Pair. 

Young. 

Pd. 

Pp. 

A. 

Pd.     Pp. 

2H  23                   

2 

5 

2 

5 

i 

3 
i 

2 
I 
I 
I 

2H  28  

4           l 
5           * 
5          3 
3          3 

2H  74. 

2H  77.     . 

21138  

2H4t    

2H44«    .. 

2H  107   ....            

Total  

Total   

'4 

6 

5 

17          8 

Expected  

Expected  

9 

3 

4 

3          i 

GROUP  III. 

GROUP  IV. 

Pair. 

Young. 

Pair. 

Young. 

Pd. 

A. 

Pd. 

2  II  2O 

3 
4 
3 
5 

2 

4 
3 

i 

i 

2 
2 
2 
2 
2 

2H  32 

5 
3 
5 
5 

2H  41 

2H  4O 

2H  440 

2H  103 

,,  Vr    

2H  118 

2H  I06 

Total 

2H  I  IQ 

2H  i4C 

Total 

24 

12 
I 

18 
all  Pd. 

Expected 

Expected  

3 

The  expected  relative  frequencies  of  these  four  sorts  of  pairs  are  as 
follows,  the  frequencies  observed  being  given  in  a  parallel  column  : 


Group. 

Expected 
frequencies. 

Observed 
frequencies. 

I 

II  

2 

Ill 

g 

IV           .            

From  this  experiment  we  get  additional  evidence  of  the  existence  of 
the  four  hypothetical  classes  of  dark-eyed  pigmented  individuals,  (i)  to 
(4),  page  48,  and  of  their  occurrence  in  something  like  the  theoretical 
proportions.  Still  further  support  for  this  view  is  afforded  by  the  third 
section  of  Darbishire's  Table  E,  page  35,  which  includes  matings  of 


COAT    CHARACTERS    IN    GUINEA-PIGS    AND    RABBITS. 


dark-eyed  animals,  each  having  one  albino  and  one  hybrid  parent. 
Half  of  these  animals  should  have  the  character  of  class  (i),  p.  48,  and 
half  that  of  class  (3) .  Pairs  established  by  random  selection  of  indi- 
viduals should,  therefore,  be  in  the  proportions,  i  mating  within  class  (i) 
to  2  matings  between  classes  (i)  and  (3)  to  i  mating  within  class  (3). 
Pink-eyed  pigmented  young  should  be  produced  only  in  matings  of  the 
first  sort,  but  albinos  should  result  from  all  three  sorts  of  matings. 
The  matings  which  produced  pink-eyed  young  are  as  follows : 


Pair 

i 

ifoung. 

Pd, 

PP> 

A. 

2H  18 

2H  27 

2H  III 

... 

2H  716  

2 

2Hi43  

2 

2H  146  

I 

2H  14.7 

aH  148  

r 

Total  

24 

JQ 

Expected  

9 

3 

4 

The  remaining  matings  are  as  follows : 


Pair. 

Young. 

Pd. 

A. 

2H  10 

4 
5 
4 
i 

4 
3 
3 

I 

2 

4 
3 

4 

i 

2 
-I 

3 

2 

3 
3 

3 
i 

2 

2H  20 

2H  22    

2H  25  

2H  26  

2H  T7.... 

2H  4C  

2H  IIO  . 

2H   112  ..  . 

2H  113  

2H  114  

2H  115    

2H  144  ... 

Total     

48 
3 

21 
I 

Expected  

The  evidence  from  the  group  of  matings  contained  in  these  two  lists 
is  less  clear  than  that  from  the  two  groups  previously  examined. 
There  is  a  considerable  excess  of  pink-eyed  young  in  most  of  the  mat- 


54  COAT   CHARACTERS    IN   GUINEA-PIGS   AND    RABBITS. 

ings  which  produced  offspring  of  that  character,  and  a  deficiency, 
almost  as  great,  of  albinos.  If  these  deviations  from  the  expected  pro- 
portions indicate  anything  other  than  a  chance  result,  it  is  an  increase  in 
the  proportion  of  gametes  bearing  the  character  pink-eye  associated 
with  pigmented  coat,  and  a  corresponding  diminution  in  the  propor- 
tion of  albino  gametes.  Yet  such  a  change  is  of  very  doubtful  occur- 
rence ;  more  probably  the  outcome  is  a  chance  one,  for  the  deficiency 
of  albinos  produced  by  the  eight  pairs  which  had  pink-eyed  young  is 
more  than  offset  by  an  excess  of  albinos  produced  by  the  other  thirteen 
pairs,  the  total  young  produced  being  121  pigmented  to  30  albinos. 

The  fact,  too,  that  certain  pairs  of  this  category  produced  no  albinos 
must  not  be  taken  as  conclusive  evidence  that  the  animals  mated  did 
not  contain  recessive  albinism.  The  expectation  is  that  only  i  in  4  of 
the  young  produced  will  be  albinos,  and  it  is  not  surprising  that,  as  a 
chance  result,  no  albinos  should  be  found  among  as  few  as  the  3  to  9 
young  produced  by  a  pair.  More  extensive  tests,  or  the  simpler  test 
of  mating  with  albinos,  would  without  doubt  have  shown  the  forma- 
tion of  albino  gametes  by  each  of  the  parents  in  question,  if  they  really 
were  of  the  parentage  indicated  in  Darbishire's  table. 

The  foregoing  considerations  indicate  that  the  correctness  of  the 
classification  of  pairs  in  the  cases  previously  examined  is  not  estab- 
lished beyond  question.  For  example,  a  pair  which  in  a  total  of  6  or 
8  young  has  produced  only  those  of  two  sorts,  might  in  subsequent  lit- 
ters produce  young  of  the  third  sort,  which  would  place  the  parents  in 

different  category.  Only  in  the  cases  where  young  of  all  three  sorts 
'have  been  produced  is  the  character  of  a  pair  conclusively  estab- 
lished. In  other  cases  the  probability  of  correctness  in  the  classifica- 
tion made  increases  with  the  number  of  young  produced.  Whatever 
errors  are  involved  tend  to  increase  the  magnitude  of  Group  IV  (pp. 
50  and  52)  at  the  expense  of  Groups  I  to  III,  and  that  of  II  and  III  at 
the  expense  of  I.  Making  all  allowance  for  such  possible  errors,  there 
would  still  seem  to  be  little  reason  to  question  the  existence,  among 
Darbishire's  dark-eyed  mice  of  generation  F,,  of  all  the  four  classes 
designated  (i)  to  (4)  on  page  48. 

The  existence  of  the  two  classes  of  pink-eyed  pigmented  mice  (5) 
and  (6),  page  48,  is  strongly  indicated  by  matings  inter  se  of  pink- 
eyed  mice  belonging  to  generation  F,,  as  recorded  by  Darbishire  in  his 
Table  H,  page  37.  According  to  our  hypothesis,  the  pink-eyed  mice 
of  this  generation  are  in  character  either  Pp  or  Pp  (Ap),  individuals 
of  the  latter  sort  being  twice  as  numerous  as  those  of  the  former.  Not 
any  of  them  contain  the  dark-eyed  character  ;  consequently  they  should 
produce  only  pink-eyed  young  or  albinos,  when  bred  inter  se.  The 


COAT    CHARACTERS    IN    GUINEA-PIGS    AND    RABBITS. 


55 


seven  pairs  tested  by  Darbishire  produced  31  pink-eyed  and  i  albino 
young,  with  no  -dark-eyed  ones — conclusive  evidence  against  the 
"  ancestry"  hypothesis  of  Gallon  and  Darbishire,  for  all  four  grand- 
parents were  dark-eyed.  The  number  of  young  produced  by  a  pair 
in  this  experiment  ranged  from  2  to  6,  the  single  albino  occurring  in  a 
litter  of  5.  This  one  albino  gives  conclusive  evidence  that  its  parents 
both  contained  recessive  albinism  and  so  were  of  class  (5).  We  should 
on  the  theory  of  probabilities  expect  the  occurrence  of  three  such  pairs 
in  seven  taken  at  random.  It  is  possible  that  more  extensive  tests  would 
actually  have  shown  the  occurrence  of  more  than  this  one,  but  it  is  a 
probability  which  amounts  almost  to  a  certainty  that  not  all  the  seven 
pairs  would  have  given  albinos,  had  they  been  more  extensively 
tested.  If  not,  then  the  occurrence  of  individuals  of  class  (6),  i.  e.,  P ' p, 
would  be  fully  established  by  the  experiment.  But  the  absence  of 
recessive  albinism  from  certain  of  the  pink-eyed  mice  of  this  genera- 
tion is  shown  in  a  simpler  way,  viz,  by  matings  with  albinos.  Nine- 
teen such  matings  are  recorded  by  Darbishire  in  his  Table  G,  page  36. 
The  number  of  young  produced  by  a  pair  ranges  from  2  to  8.  Five  of 
the  nineteen  pairs  produced  albino  young,  showing  that  they  contained 
recessive  albinism  and  transmitted  it  in  approximately  half  their 
gametes,  for  the  young  produced  by  these  pairs  are  12  pigmented  to  12 
albino.  Since  the  remaining  fourteen  pairs  produced  not  a  single 
albino  in  a  total  of  74  young,  it  is  certain  that  many  if  not  most  of 
them  did  not  form  albino  gametes,  for  had  they  done  so  half  their 
young  should  have  been  albino.  The  albino  parents  used  in  this 
test  evidently  all  transmitted  latent  the  black-eyed  character,  for  every 
one  of  the  nineteen  pairs  produced  dark-eyed  young,  showing  that  the 
albino  parent  was  either  of  class  (8),  page  48,  or  possibly  of  class  (7). 
The  occurrence  of  an  albino  of  this  latter  class  (one  which  transmits 
latent  in  half  its  gametes  the  dark-eyed  character,  but  in  the  other  half  the 
pink-eyed  character)  is  shown  beyond  question,  in  Darbishire's  Table 
G,  by  a  mating  (2/7  120)  which  produced  2  dark-eyed  and  i  pink-eyed 
young.  The  occurrence  of  albinos  which  may  have  been  either  of 
class  (7),  page  48,  or  of  class  (9)  (/.  £.,  which  transmitted  the  pink- 
eyed  character  either  in  half  or  in  *11  of  their  gametes)  is  indicated  by 
three  pairs  in  Darbishire's  Table  F,  page  36,  as  follows : 


Voung 

Pd. 

Pp. 

A. 

K  10                   

i 

2 

K  ii               

i 

2 

j 

K  ic 

3 

3 

56  COAT    CHARACTERS    IN    GUINEA-PIGS    AND    RABBITS. 

In  this  experiment  the  parents  both  belonged  to  generation  F;,  and 
were  respectively  a  dark-eyed  animal — which  might  be  taken  from  any 
of  the  classes  (i)  to  (4),  p.  48 — and  an  albino — which  might  be  taken 
from  any  of  the  three  classes  (7)  to  (9).  We  should,  on  the  theory 
of  probabilities,  expect  half  the  eighteen  pairs  enumerated  in  Darbi- 
shire's  Table  F  as  producing  pigmentcd  young  to  produce  pink-eyed 
offspring.  Only  three,  as  stated,  gave  this  result,  instead  of  the  expected 
nine.  But  the  number  of  young  produced  by  several  of  the  pairs 
was  very  small,  being  in  four  cases  3,  and  matings  which  should  pro- 
duce less  than  I  in  4  of  pink-eyed  young  (viz,  3  in  16)  may  well  have 
failed  to  produce  any  in  litters  of  4  or  less.  In  the  three  matings  cited 
it  is  evident  that  both  parents  formed  gametes  bearing  the  pink-eyed 
character,  since  pink-eyed  young  were  produced.  Accordingly  the 
dark-eyed  parent  must  have  belonged  either  to  class  (i)  or  to  class  (2), 
and  the  albino  parent  either  to  class  (7)  or  to  class  (9).  In  mating 
K  10,  the  dark-eyed  parent  was  probably  of  class  (2),  since  no  albino 
young  were  produced,  though  the  small  number  of  young,  three,  leaves 
this  uncertain  ;  but  in  matings  K  1 1  and  K  15,  it  is  clear  that  the  dark- 
eyed  parent  was  of  class  (i ) ,  since  albino  young  were  produced  in  both 
cases.  There  is  nothing  to  indicate  whether  the  albino  parents  in  these 
three  matings  were  pure  or  hybrid  as  regards  the  pink-eyed  character, 
except  the  large  proportion  of  pink-eyed  young  produced,  which  would 
indicate  that  they  were  probably  of  class  (9),  i.  e.,  pure. 

Accordingly,  in  Darbishire's  experiments,  we  lack  strong  evidence 
by  breeding  test  of  the  occurrence  of  this  class  (9)  only  of  all  those  in- 
dicated on  page  48.  Yet  I  doubt  not  that  the  single  albino  born  of  pink- 
eyed  parents,  as  recorded  in  Darbishire's  Table  H,  page  37,  if  tested 
would  prove  to  be  of  this  sort,  i.  e.,  lacking  entirely  the  dark-eyed 
character,  so  that  when  mated  with  pink-eyed  animals  only  pink-eyed 
offspring  would  be  produced.  This  result  would  be  parallel  with  what 
in  mice  Allen  ( :  04)  observed  to  be  the  relation  of  chocolate  and  choco- 
late-yellow pigmentation  to  albinism,  and  what  I,  in  guinea-pigs,  have 
shown  to  be  the  relation  of  red  and  of  yellow  pigmentation  to  albinism. 

HEREDITY  OF  ROUGH  COAT. 

In  certain  varieties  of  the  domesticated  guinea-pig  the  hair  has  a  very 
peculiar  arrangement,  sloping  away  in  all  directions  from  certain  points, 
which  are  situated  for  the  most  part  symmetrically  along  the  sides  of 
the  body,  nearly  coinciding  with  the  centers  of  the  typical  pigment 
patches.  As  a  consequence  the  animal  seems  covered  with  cowlicks  or 
rosettes,  between  which  the  hair,  sloping  in  opposite  directions,  forms  a 
series  of  ridges  or  crests.  These  are  best  seen  in  the  so-called  Abys- 
sinian (the  short-haired  but  rough)  variety.  (See  PI.  2,  figs.  3  and  4.) 


COAT    CHARACTERS    IN    GUINEA-PIGS    AND    RABBITS.  57 

When  the  rough  coat  character  is  best  developed,  rosettes  are  seen 
around  the  following  paired  centers:  (i)  The  eye,  (2)  a  point  immedi- 
ately behind  the  ear,  (3)  the  shoulder,  (4)  a  point  dorso-lateral  on  the 
side  of  the  body  about  midway  between  shoulder  and  hip,  (5)  the  hip, 
(6)  the  groin,  (7)  each  of  the  single  pair  of  mammae;  and  from  two 
unpaired  centers,  viz,  (8)  the  middle  of  the  forehead,  and  (9)  the  navel. 
The  direction  of  the  hair  is  also  reversed  on  the  toes. 

In  crosses  between  pure  rough  individuals  and  smooth  ones,  the  rough 
character  is  dominant,  all  the  young  being  rough  and  ordinarily  having 
the  rough  character  as  fully  developed  as  in  the  rough  parent.  jBut 
certain  smooth  animals,  which  may  properly  be  described  as  prepotent, 
produce  offspring  which  show  a  weakened  condition  of  the  rough  char- 
acter, some  of  the  typical  rosettes  being  either  less  well  developed  than 
in  the  rough  parent  or  wanting  altogether  (see  PI.  6,  fig.  12).  Such 
offspring  may  be  called  partial  rough.  They  frequently  transmit  the 
rough  character  in  its  full  intensity  to  their  offspring,  as  we  shall  pres- 
ently see,  though  they  themselves  are  only  partially  rough. 

Repeated  crossing  of  rough  animals  with  prepotent  smooth  ones 
results  in  further  weakening  of  the  rough  character  until  it  is  almost 
eliminated.  Successive  stages  in  this  weakening  process  may  be  recog- 
nized, which  are  about  as  follows  : 

Condition  A:  The  fully  developed  rough  character  as  above  de- 
scribed (see  PI.  2,  figs.  3  and  4). 

Condition  B  :  Forehead  and  shoulder  rosettes  have  disappeared,  hip 
and  side  rosettes  either  fuse  into  an  obliquely  longitudinal  dorso-lateral 
part  sloping  downward  posteriorly,  or  the  hip  center  disappears  entirely. 

Condition  C  (PI.  6,  fig.  12)  :  The  only  conspicuous  rosettes  are  the 
side  rosettes,  though  the  ear  rosettes  may  usually  be  found  by  careful 
examination  ;  between  the  ear  and  side  rosettes  a  ridge  runs  obliquely 
downward  and  backward  across  the  body  from  the  shoulder ;  there  is 
likewise  a  median  dorsal  crest ;  the  hair  is  reversed  in  direction  on  the 
hind  feet,  and  turned  laterally  but  not  reversed  on  the  front  feet. 

Condition  D  :  Only  a  single  pair  of  rosettes,  the  side  rosettes,  persist ; 
a  mid-dorsal  crest  extends  from  the  head  back  to  the  rump  ;  hair  on  the 
feet  as  in  Condition  C,  or  that  of  the  front  feet  straight. 

Condition  E :  No  rosettes,  a  mid-dorsal  crest  from  the  head  back- 
ward, perhaps  half  the  length  of  the  body ;  hair  of  toes  reversed  on 
hind  feet  only  or  not  at  all. 

Condition  F  :  No  rosettes  or  crest.     Hair  reversed  on  hind  feet  only.  \ 

It  must  not  be  understood  that  these  steps  are  necessarily  taken  one  \ 
at  a  time.  The  original  cross  between  rough  and  smooth  may  lead  I 
directly  from  Condition  A  to  Condition  D,  when  the  smooth  parent  it  / 
very  prepotent. 


COAT    CHARACTERS    IN    GUINEA-PIGS    AND    RABBITS. 


The  matings  which  have  been  made  between  pure  rough  parents 
and  smooth  ones  may  be  summarized  as  follows : 


Parentage. 

Young,  in  appearance. 

R. 

PR. 

Sm. 

R  c?  1516  x  Sm.  9  9  

12 

8 
"3 

2 
3' 

166 

5 
ii 

4 

20 

1"  — 

R    c?  1586  X  Sm    9  9 

R   tf  2002  x  Sm.  9  9  

R.  9  2040  x  Sm.  cf  2060  
R    C?  2°59  X  Sm    9  9 

Total 

[Abbreviations  :  tf.  -  rough  ;  PR.  =  partial  rough  ;  .S'wr.  =  smooth.] 

It  will  be  observed  that  every  one  of  the  186  young  produced  by  this 
experiment  bears  the  rough  character,  all  but  20  of  them  having  it  fully 
developed  (Condition  A)  ;  the  character  of  the  exceptional  20  partial- 
rough  animals  varies  from  Condition  B  to  Condition  D. 

PREPOTENCY  AND  DOMINANCE. 
The  matings  which  produced  the  20  partial-rough  young  are  of  par- 
ticular interest.     In  detail  they  are  as  follows : 


Young. 

R. 

PR. 

5m. 

Sm.  9  ao8  (or  996?)  X  R  .  cf  2002  
Sm.  9  2005  X  R-  (jf  2002  

2 

4 

Sm.  9  2005  X  R.  tf  2059  

Sm.  9  2056  X  R.  tf  2002  

Sm.  9  2056  x  R.  cT  2059  

Sm.  9  1344  x  /?.  cf  1516  

Sm.  9  1499  X  R.  tf  1516  

The  partial  rough  young,  it  will  be  noticed,  were  all  produced  by 
five  (or  possibly  six)  mothers.  Unfortunately,  there  is  some  uncertainty 
as  to  the  mother  of  the  first  of  the  lots  of  young  enumerated.  The  two 
females  (9  208  and  9  996)  had  6  young  together  at  the  same  time,  and 
so  it  was  impossible  to  separate  the  young  by  litters,  but  from  the  color- 
ation and  size  of  the  young  I  think  it  probable  that  9  208  was  the 
mother  of  the  4  partial-rough  young.  But  9  996  was  of  the  same 
smooth  stock  as  9  208,  and  it  would  not  be  surprising  if  her  gametes 
had  a  similar  potency.  Unfortunately,  no  further  tests  with  these 
mothers  could  be  made,  for  they  both  died  soon  after  producing  the 
young  enumerated.  The  two  females,  9  2005  and  9  2056,  were  both 
mated  with  the  same  rough  males  (d*  2002  and  d1  2059).  The  former 
produced  only  partial-rough  young  by  both  males ;  the  latter  produced 


COAT   CHARACTERS    IN    GUINEA-PIGS    AND    RABBITS.  59 

some  fully  rough  and  some  partial-rough  young  by  both  males.  From 
these  cases  it  seems  clear  that  the  production  of  partial- rough  young 
was  due  to  some  unusual  potency  of  the  gametes  bearing  the  smooth 
character,  and  that  this  potent  character  was  inherent  in  all  the  gametes 
formed  by  9  2005,  but  in  only  about  half  of  those  formed  by  9  2056. 
If  9  208  was,  as  supposed,  the  mother  of  the  4  young,  all  partial-rough  in 
character,  then  she  probably  formed  only  potent  gametes,  as  did  9  2005 
apparently  ;  but  if  9  208  and  9  996  each  produced  some  of  the  partial- 
rough  and  some  of  the  fully-rough  young,  then  they  were  both  similar  in 
character  to  9  2056,  as  regards  the  formation  of  potent  gametes.  It 
would  seem  probable,  accordingly,  that  potency  of  the  sort  under  consid- 
eration is  a  function  of  the  gametes  ;  that  while  most  smooth  females  form 
no  potent  gametes,  some  form  50  per  cent  and  some  100  per  cent  of  such 
gametes  ;  or,  in  other  words,  that  some  smooth  animals  are  purely  potent, 
others  hybrid,  as  regards  potency,  but  a  majority  «o»-potent. 

;The  question  now  arises,  is  this  potency  handed  on  from  generation 
o  generation,  /.  e.,  do  the  gametes  remain  pure  as  regards  potency,  or 
s  their  potency  affected  by  a  cross  with  the  alternative  and  dominant 
character,  rough  coat.  There  is  some  evidence  in  favor  of  both  these 
ideas.  On  one  hand  there  is  a  manifest  tendency  for  gametes  to  retain 
from  generation  to  generation  any  abnormal  potency  which  they  may 
possess  ;  but  on  the  other  hand  cross-breeding  probably  does  frequently 
alter  the  potency  of  recessive  gametes. 

The  first  of  the  two  ideas  just  mentioned  receives  support  from  the 
admirable  experiments  of  Coutagne  (  :  02)  with  silk-moths,  which 
seem  to  have  received  less  attention  than  is  warranted  by  their  great 
richness  in  results  and  the  care  with  which  they  have  been  executed. 
Coutagne  crossed  two  distinct  races  of  silk-moths,  one  of  which  pro- 
duced only  white  cocoons,  the  other  only  yellow  cocoons.  Dominance 
apparently  was  alternative  between  the  two  characters,  which  seem  to 
have  been  nearly  equal  in  potency,  so  that  sometimes  one,  sometimes 
the  other  dominated.  The  cocoons  were  219  white  in  character,  340 
yellow,  without  intermediates.  Images  hatching  from  either  sort  of 
cocoon,  when  mated  inter  se,  produced  the  other  sort  of  cocoon,  as 
well  as  that  from  which  they  hatched,  and  approximately  in  the  pro- 
portions 3  of  their  own  sort  to  i  of  the  other.  Thus,  moths  hatch- 
ing from  white  cocoons  mated  inter  se,  and  moths  hatching  from  yel- 
low cocoons  mated  inter  se,  produced  in  different  lots — 
From  white  cocoons  :  TOTAL. 

White 339    87     180         606 

Yellow 140    36     109         285 

From  yellow  cocoons  : 

White 120    34      80         334. 

Yellow 44i     89    236         766 


6o 


COAT   CHARACTERS    IN   GUINEA-PIGS    AND    RABBITS. 


Evidently  there  is  a  strong  tendency  for  white,  when  it  dominates  in 
a  first  cross,  to  behave  as  a  dominant  also  among  the  progeny  of  that 
cross ;  and  likewise  for  yellow,  when  it  dominates  in  a  first  cross,  to 
behave  as  a  dominant  among  the  progeny  of  that  cross.  This  indicates 
clearly  the  persistence  from  generation  to  generation  of  relative  poten- 
cies of  gametes  of  a  particular  sort.  As  regards  the  relative  proportions 
of  white  and  of  yellow  cocooned  young,  it  is  noteworthy  that  there  is 
throughout  the  experiment  a  slight  excess  of  yellows  over  the  expected, 
indicating  a  somewhat  superior  potency  of  that  character,  which,  in 
matings  between  other  white-cocooned  and  yellow-cocooned  races,  was 
found  to  be  uniformly  dominant. 

That  cross-breeding  may  modify  the  relative  potencies  of  gametes 
seems  highly  probable,  yet  the  evidence  for  this  idea  at  present  avail- 
able is  inconclusive.  It  consists  principally  in  an  observed  excess  of 
partial-rough  young  over  the  expected  proportion  in  certain  matings, 
which  will  presently  be  described,  but  the  numbers  of  young  as  yet 
produced  in  these  experiments  are  too  small  to  be  at  all  conclusive. 

One  mating  of  pure  rough  animals  (/?.  cT  2002  X  /?.  9  2003)  Pr°- 
duced,  as  expected,  only  rough  young,  five  in  number  (see  p.  63). 

Hybrid  rough  animals,  R.  (Sm.),  when  mated  with  pure  rough 
animals,  have  produced,  as  expected,  only  rough  young,  57  being  fully 
rough  (Condition  A,  p.  57)  and"  i  partial-rough  (Condition  B  or  C). 

The  one  partial-rough  animal  occurred  in  a  litter  of  three  young  borne 
by  R.  9  2040  mated  with  hybrid  R.  (Sm.)  tf  994.  This  female  had 
previously  borne  two  fully  rough  young  by  Sm.  d*  2060  (see  p.  58). 
It  is  probable,  therefore,  that  the  hybrid  c?  994  did  form  some  smooth 
gametes  of  unusua?- potency,  though,  unfortunately,  he  was  not  tested  by 
other  matings  with  rough  females. 

Hybrid  rough  animals,  R.  (Sm.)  in  character,  when  mated  with 
smooth  ones,  have  produced  127  rough  young  and  146  smooth  ones, 
equality  of  the  two  classes  being  expected  on  the  Mendelian  hypothesis 
of  segregation.  Of  the  1 27  rough  young,  all  except  6  have  Condition 
A,  the  fully  rough  coat.  The  6  partial-rough  young  were  produced  in 
four  different  litters,  each  by  a  different  pair.  They  were  as  follows  : 


Parentage. 

Young, 
in  appearance. 

R. 

PR. 

Sm. 

R.  (Sm.)  $  mi  X  Sm    9  644  . 

3 
i 

3 

R.  (Sm.  )  cT  1178  X  Sm.  Q  1661 

i 

R.  (Sm.)  rf  1332  X  Sm.  9  1338 

R.  (Sm.)  9  2034  X  Sm.  ^  1147  ... 

... 

COAT    CHARACTERS    IN    GUINEA  PIGS   AND    RABBITS.  6l 

The  smooth  animals  used  in  these  matings  were  all  pure-bred  except 
9  1338,  which  had  a  hybrid,  R.  (Sm.),  father,  but  a  pure-bred  smooth 
mother.  We  can  not  assume,  however,  that  these  hybrid  rough  ani- 
mals formed  in  general  weak  rough  gametes,  for  R.  (Sm.)  cJ1  1111  had 
in  all,  by  smooth  females,  13  rough  offspring,  but  only  in  the  mating 
with  9  644  was  a  partial-rough  individual  produced  ;  again  R.  (Sm.) 
c?  1 178  had  rough  offspring  (6  in  all)  by  three  different  smooth  females, 
but  only  in  the  mating  with  $  1661  did  he  produce  a  partial-rough 
animal.  It  would  seem  that  the  degree  in  which  dominance  is  realized^ 
in  the  zygote  is  dependent  upon  the  relative  potency  of  the  gametes] 
uniting,  and  that  potency  is  apt  to  be  more  variable  in  the  gametes  oi/ 
cross-bred  than  in  that  of  pure-bred  animals.  If  so,  hybrid  rough  ani- 
mals bred  inter  se,  or  with  cross-bred  rough  or  smooth  individuals, 
should  produce  an  especially  large  proportion  of  partial-rough  young. 
The  experiments  made  are  as  yet  hardly  extensive  enough  to  give  a 
decisive  answer  to  this  question. 

Fully  rough  hybrid,  R.  (-Szw.),  animals  bred  inter  se,  have  produced 
in  all  32  rough  young,  only  one  of  which  is  a  partial-rough.  This  one 
was  produced  by  the  following  mating  : 

R.  (Sm.}  J1  mi  X  R.  (Sm.)  9  1438,  produced  i  R.,  i  PR.,  2  Sm. 

This  same  male,  it  will  be  remembered,  produced  a  partial-rough  indi- 
vidual by  the  smooth  female  644. 

We  may  return  now  to  the  question  whether  the  condition  of  unusual 
potency  in  the  smooth  gametes  of  animals  producing  partial-rough 
young  is  handed  on  to  the  posterity  of  those  animals.  If  the  partial- 
rough  character  of  hybrid  animals  is  due  simply  to  :mperfectly  realized 
dominance  of  the  character  borne  by  the  dominant  gamete,  and  if  the 
characters  united  in  the  zygote  maintain  their  distinctness  and  segre- 
gate with  the  same  relative  potencies,  when  gametes  are  formed  by 
the  hybrid  as  they  possessed  before,  then  we  should  expect  to  get  fully 
rough,  as  well  as  partial-rough  offspring,  by  mating  partial-rough 
animals  either  inter  se  or  with  rough  animals.  The  result  of  mating 
partial-rough  with  smooth  animals  would  depend  upon  the  relative 
potency  of  the  gametes  formed  by  the  smooth  mates  ;  if  none  of  their 
gametes  were  unusually  potent,  then  the  offspring  should  be  half  fully 
rough  and  half  smooth,  without  partial-rough  young.  But  if  half 
the  gametes  formed  by  the  smooth  animals  are  unusually  potent,  then 
the  offspring  should  be  visibly  as  i  R.  to  i  PR.  to  2  Sm. 


62 


COAT    CHARACTERS    IN   GUINEA-PIGS    AND    RABBITS. 


Matings  of  these  three  sorts  show  the  following  results.  The  "  ex- 
pected "  results  are  calculated  on  the  hypothesis  of  persistent  relative 
potencies  and  full  segregation  of  the  rough  and  smooth  characters. 


Parentage. 

Young,  in  appearance. 

Observed. 

Expected. 

7?. 

PR. 

Sm. 

It. 

/Ve. 

£M. 

I.—  PR.  (Sm.}  x  PR.  (Sm.}  : 

i 

i 

2 
3 

3 

2 

... 

r?  1987  X    9   1268 

2 

Total                            

6 

2 

5 

4 

10 
2 

3 

10 

5 

\\.-PR.  (Sm.)  X  /?.  (Sm.): 

rP  Il6o  X    Q  OQI 

... 

... 

i 

... 

... 

... 

Total                          

i 

6 
i 

2 
2 

4 

*i 

*i 

III.—  PR.  (Sm.*)  X  (Sm.): 

i 

I 

3 

.. 

... 

... 

; 

o   'j™  ^   *  *->w 

i 
i 

i 
i 

.. 

... 

... 

1 

2 

3 

... 

* 

Total                        

4 

4 

U 

Si-"* 

o-5* 

10} 

The  agreement  between  the  observed  and  the  expected  proportions 
of  fully  rough  (/?.)  and  partial-rough  (PR.)  offspring  is  sufficiently 
close  to  lend  support  to  the  hypothesis  of  persistent  gametic  potency 
from  generation  to  generation.  For  on  the  alternative  hypothesis,  that 
partial-rough  hybrid  animals  form  only  partial-rough  gametes  and 
smooth  ones,  no  animals  with  the  fully  developed  rough  character 
should  be  formed  either  in  Group  I  or  Group  III  of  the  foregoing 
matings,  but  we  see  that  young  of  this  sort  were  produced  in  all  these 
groups.  Yet  it  is  probable  that  cross-breeding  must  be  recognized  as 
an  element  which  may  modify  the  potencies  of  gametes,  causing  those 
of  a  cross-bred  individual  to  be  less  uniform  in  potency  than  those  of 
an  animal  not  so  crossed.  Further  experiments  are  needed  to  throw 
light  on  this  question. 


COAT    CHARACTERS    IN    GUINEA-PIGS    AND    RABBITS.  63 

Leaving  out  of  consideration  the  degree  in  which  the  rough  character 
is  developed  in  the  coat  of  hybrid  offspring,  we  may  inquire  how  nearly 
the  Mendelian  proportions  of  rough  and  smooth  young  are  approxi- 
mated. This  will  be  plain  from  an  examination  of  the  following  table  : 


Nature  of  mating. 

Young. 

Observed. 

Expected. 

Rough. 

Smooth. 

Rough. 

Smooth. 

Rough  x  rough  

53 

'35 

^_437 
6: 

»9 
159 

~78~ 

15 

J 

54 
H7 

450 

... 

is 
M7 

~65~ 

Rough  x  rough  (smooth).     .....  .  . 

Rough  x  smooth  

Rough  (smooth)  x  rough  (smooth). 
Rough  (smooth)  x  smooth  

Total  

6i5 

As  in  the  case  of  albinism,  there  are  a  few  more  recessive  individuals 
than  are  expected.     This  may  be  purely  a  chance  result,  or  it  may  be 
due  to  superior  fertility  of  the  recessive  gametes ;  but  a  different  expla- 
nation is  suggested  by  an  observation  which  will  presently  be  stated. 
The  suggested  explanation  is  that  the  excess  of  recessive  individuals 
may  be  due  to  latency  of  the  rough  character  in  certain  individuals 
apparently  smooth.     That  such  latency  is  possible  is  shown  by  the 
sudden  appearance  in  one  of  my  families  of  smooth  animals  of  a  partial 
rough  individual,  9  969,  having  a  well-marked  crest  extending  from 
the  head  to  the  middle  of  the  back  and  conspicuous  though  imperfectly 
developed  side  rosettes.     The  ancestors  of  this  female  for  at  least  three 
generations  had  been  ordinary  smooth  individuals,  though  it  is  possible 
that  one  or  more  of  these  may  have  had  a  slight  crest  in  the  region  of 
the  shoulders;  for  I  found  that  a  brother  of  9    969,  viz,  c?  971,  had 
such  a  crest,  though  it  could  be  detected  only  by  very  careful  examina- 
tion.   Unfortunately  most  of  the  ancestors  had  died  before  my  attention 
was  called  to  this  case.     The  father's  skin,  which  I  have,  shows  no 
indication  of  a  crest,  though  possibly  it  might  have  done  so  before  it 
was  dried.     The  partial-rough  9  969  had  by  the  brother  mentioned, 
c?  971,  four  young,  one  of  which  was  a  partial-rough  like  herself,  the 
others   being   smooth.     Clearly,  then,  she  both  possessed  the  rough 
character  in  a  state  of  partial  activity  and  was  able  to  transmit  it  in 
this  condition  to  her  offspring,  though  in  her  ancestors  it  must  have 
been  present  in  a  state  of  almost,  if  not  quite  complete  latency.     Very 
likely  suitable  matings  of  the  mother  would  restore  the  rough  character 
in  certain  of  her  offspring  to  a  condition  of  full  activity.     Further 
experiments  with  this  animal  are  now  in  progress. 


64  COAT   CHARACTERS    IN    GUINEA-PIGS    AND    RABBITS. 

If  I  have  interpreted  correctly  the  partial-rough  animals  obtained  in 
my  experiments,  they  may  be  similar  in  nature  to  centripetally  pig- 
mented  animals  which  lack  some  of  the  typical  pigment  patches,  or 
have  only  the  eyes  pigmented.  A  cross  with  albinos  in  which  cen- 
tripetal pigmentation  is  latent  may  serve  to  call  the  full  set  of  coat  spots 
into  activity,  producing  fully  pigmented  young,  as  we  have  already  seen. 
Similarly  we  may  expect  that  crossing  a  partial-rough  animal  with  a 
smooth  animal  in  which  the  rough  character  is  fully  latent  would  call  the 
rough  character  into  full  activity  in  the  offspring.  It  remains,  however, 
to  demonstrate  the  existence  of  smooth  animals  contain mgfu/ly  latent 
the  rough  character.  I  have  as  yet  no  evidence  of  their  existence  other 
than  the  slight  excess  of  smooth  animals  over  the  expected  proportion. 

HEREDITY  OF   LONG  COAT. 

The  longest  or  contour  hairs  of  ordinary  domesticated  guinea-pigs, 
like  those  of  the  wild  Cavia  aperea,  do  not  exceed  a  length  of  about  4 
centimeters,  but  domesticated  varieties  with  hair  many  times  that  length 
are  now  well  known.  Where  or  when  they  originated  is  unknown  ; 
according  to  Cumberland  they  would  seem  to  have  been  introduced  into 
England  from  France  ;  our  American  stocks  probably  came  from  Eng- 
land. Long-haired  smooth  animals  are  commonly  called  "Angoras," 
and  long-haired  rough  ones  "  Peruvians."  But  the  two  sets  of  charac- 
ters (long  vs.  short,  and  smooth  vs.  rough)  are  entirely  independent  of 
each  other,  as  we  shall  see,  so  that  for  the  present  we  shall  consider  only 
the  length  of  the  coat,  irrespective  of  whether  it  is  rough  or  smooth. 

My  first  experience  with  long-coated  guinea-pigs  was  wholly  un- 
premeditated. In  a  family  of  short-haired  guinea-pigs  with  which  I 
was  experimenting  and  was  practicing  close-breeding,  there  appeared 
several  animals  whose  contour  hairs  were  about  twice  as  long  as  those 
of  their  parents.  These  animals  were  all  descended  from  a  single  pair 
of  short-haired  guinea-pigs  which  had  been  purchased  from  a  breeder, 
but  which  I  have  no  doubt  had  numbered  among  their  ancestors  a 
long-haired  animal.  I  found  that  the  long-haired  young  bred  true 
inter  se,  which  indicated  that  the  long-haired  character  was  recessive 
in  nature  in  relation  to  normal  or  short  coat.  This  idea  has  been  fully 
confirmed  by  subsequent  experiments,  which  were  systematically  insti- 
tuted with  the  longest  haired  animals  which  I  could  secure. 

In  studying  the  inheritance  of  this  character,  it  is  necessary  to  rear 
the  young  to  an  age  of  about  two  months  before  one  can  be  sure 
whether  they  are  to  have  a  normal  coat,  or  one  of  more  than  normal 
length.  For  at  birth  guinea-pigs  of  all  sorts  have  hair  of  about  the 
same  length  (2  cm.).  The  coat  of  short-haired  guinea-pigs  reaches  its 
maximum  length  (about  4  cm.)  not  far  from  the  age  of  one  month,  and 


COAT    CHARACTERS    IN   GUINEA-PIGS    AND    RABBITS.  65 

is  then  gradually  shed.  On  the  other  hand,  the  hair  of  long-coated  ani- 
mals apparently  is  not  shed  at  this  period,  but  keeps  on  growing. 
At  two  months  of  age  it  is  5  to  7  cm.  long,  at  three  months  it  is  6  to 
9  cm.  long.  In  the  period  from  three  to  four  months  of  age  is  another 
critical  stage.  Animals  which  begin  to  shed  their  longest  hair  at  this 
period  apparently  do  not  acquire  a  longer  coat  at  any  period  of  their 
subsequent  life,  but  continue  to  have  one  whose  maximum  length  is  about 
8  cm.  But  animals  which  pass  the  age  of  about  four  months  without 
shedding  their  longest  hairs  increase  the  length  of  their  coat  rapidly, 
so  that  they  may  have  a  coat  of  10  to  12  cm.  maximum  length  when  four 
to  five  months  old,  and  one  of  14  to  16  cm.  at  six  to  seven  months. 

The  acquisition  of  an  abnormally  long  coat  is  due,  accordingly,  not 
to  unusually  rapid  growth  of  the  hair,  but  to  a  peculiar  mode  of  growth. 
The  hairs  of  a  normal  animal  are  thick  and  stiff  in  the  middle,  but  taper 
toward  either  end,  somewhat  like  the  quills  of  a  porcupine.  In  the 
middle  of  the  hair  the  medulla  is  very  thick,  but  it  diminishes  gradually 
toward  either  end,  where  it  is  wanting  altogether.  A  hair  of  this  sort, 
then,  is  the  result  of  a  definite  growth  cycle  in  the  hair  follicle,  this 
cycle  covering  apparently  about  two  months'  time,  though  my  observa- 
tions on  this  point  are  yet  imperfect.  When  a  hair  is  completed,  after 
attaining  a  length  of  about  4  cm. ,  a  new  one  apparently  is  formed  below 
it  and  crowds  the  old  one  out.  But  in  the  long-haired  animal,  the 
termination  of  a  two-months  growth  cycle  is  frequently,  if  not  regularly, 
omitted.  The  hair  is  more  nearly  of  uniform  thickness  throughout  its 
length,  and  is  not  narrowed  to  a  base  at  the  end  of  a  single  period  of 
two  months,  but  grows  without  interruption  during  two,  three,  or  four 
such  periods. 

For  this  reason,  as  I  have  observed,  hair  measurements  of  long- 
coated  animals  do  not  form  a  continuous  series,  but  tend  to  group 
themselves  about  mean  maximal  lengths  as  follows: 

(1)  8  cm.,  double  the  length  of  normal  or  short  coat,  not  attained 
under  three  months  of  age. 

(2)  12  cm.,  three  times  the  length  of  short  coat ;  not  attained  under 
five  months  of  age. 

(3)  16  cm.,  four  times  the  length  of  short  coat;  not  attained  under 
seven  months  of  age. 

Coats  longer  than  this  I  have  not  had  an  opportunity  to  study,  though 
such  are  said  to  occur. 

That  long-haired  animals  bred  inter  sc  produce  only  long-haired    1 
young  is  shown  by  the  following  experiment :  Six  different  long-haired 
males  (viz,  955,  1586,  PI.  5,  fig.  9,  1709,  2002,  PI.  I,  fig.  i,  and  2060,    / 
pl-  3i  %•  5)  nave  been  mated  with  19  different  long-haired  females,  / 
producing  49  young,  all  long-haired.     There  were  produced  also 


66 


COAT    CHARACTERS    IN    GUINEA-PIGS    AND    RABBITS. 


ral  young  which  died  before  their  coat-character  could  be  determined, 
but  all  those  which  survived  had  hair  much  longer  than  that  of  the 
ordinary  short-haired  animal. 

Further  evidence  of  the  recessive  nature  of  long  coat  is  afforded  by 
matings  between  long-haired  and  short-haired  animals.  Long-haired 
c?  2002  (PI.  i,  fig.  i),  whose  coat  measures  14-17  cm.,  according  to 
condition,  has  been  mated  with  14  different  short-haired  females,  pro- 
ducing 58  young,  all  of  which  have  hair  under  5  cm.  in  length. 
Nevertheless,  the  influence  of  the  long-haired  parent  is  frequently  seen 
in  increased  softness  of  the  coat,  though  this  is,  as  a  rule,  not  longer 

rthan  in  the  short-haired  parent. 

When  two  long-haired  animals  are  mated,  one  of  which  has  longer 
hair  than  the  other,  the  offspring  have  a  coat  like  that  of  the  shorter- 
haired  parent,  usually  without,  though  sometimes  with,  interspersed 
hairs  of  greater  length  (PI.  6,  fig.  1 1 ) .  In  other  words  there  is  a  strong 
tendency  for  the  shorter  coat  to  dominate  in  all  cases  over  the  longer  one. 
Accordingly,  evidence  for  the  dominance  of  short  coat  in  crosses 
with  long  coat  is  fairly  complete ;  the  evidence  for  the  occurrence  of 
segregation  in  the  next  generation  is  less  satisfactory,  for,  though  there 
occur  among  the  offspring  good  long-coated  and  good  short-coated 
individuals,  others  show  a  poor  development  of  the  long  coat,  and  the 
whole  number  of  long-coated  animals  exceeds  that  expected.  Thus 
hybrids,  Sh.  (.£•)*  in  character,  mated  inter  se^  have  produced  thus  far 
13  Sh.  to  7  Z.,  where  3  Sh.  to  i  L.  are  expected,  and  long-haired  animals 
when  mated  with  hybrids,  Sh.  (Z.),  for  the  most  part  children  of  <? 
2002  (see  PI.  i,  fig.  i)  have  produced  36  Sh.  to  65  Z,.,  or  nearly  twice 
as  many  long-haired  as  short-haired  young,  where  equality  of  the  two 
sorts  is  expected.  These  young  have  been  born  to  seven  different  long- 
haired parents,  and  the  excess  of  long-haired  offspring  appears  among 
the  young  of  all  except  two  of  them,  as  follows  : 


Parents. 

Young. 

Long-haired. 

Short-haired  {Long). 

Short. 

Long. 

J»  206  

<?73^-  
c?  1586. 

99  
9  9  
0  iGoS 

5 
5 
o 

2 

9 
o 

»5 

S 
9 

4 

18 
3 
25 

(?  I7OQ 

O    1770 

C?  2002  
O    2O4O.   .. 

9  9  

d*  206?..  ..:::::::::::: 

Total  

9  9  

36 

65 

*  L.  =  long-haired,  Sh.  =  short-haired. 


COAT    CHARACTERS    IN   GUINEA-PIGS    AND    RABBITS.  67 

The  departure  here  from  the  expected  equality  of  the  two  classes  is 
too  great  and  too  uniform  to  be  referable  to  chance.  It  would  seem 
probable,  rather,  that  fewer  gametes  are  formed  bearing  the  character 
short-coat  than  are  expected.  This  maybe  due  either  to  failure  of  con- 
trasted characters  to  segregate  at  gamete  formation  in  certain  cases,  or 
possibly  to  partial  latency  of  the  character  short-hair  in  gametes  which 
transmit  active  the  character  long-hair,  the  resultant  being  an  interme- 
diate condition.  Further  experiments  are  needed  to  show  which  of  these 
two  ideas  is  correct,  though  at  present  the  former  seems  more  probable. 

Short-haired  females  obtained  by  mating  a  primary  hybrid,  Sh.  (£.), 
with  a  pure  short-haired  animal  have,  in  several  cases,  been  mated 
with  the  long-haired  males,  2002  (PL  i,  fig.  i)  and  2060  (PI.  3,  fig.  5). 
It  is  expected  that  half  of  such  females  will  contain  recessive  the  charac- 
ter long-coat,  and  that  half  will  be  free  from  it,  z'.  e.,  will  produce  only 
short-haired  young.  The  outcome  shows  that  9  out  of  12  females 
tested  contain  recessive  the  character  long-coat,  for  they  produce  long- 
coated  young.  This  is  another  bit  of  evidence  that  segregation 
occurred  less  often  than  expected  in  the  gametes  of  the  primary  hybrids, 
though  it  throws  no  doubt  on  the  uniformly  dominant  character  of 
short-coat.  Again,  the  nine  extracted  hybrids,  which  contain  reces- 
sive the  character  long-coat,  should,  when  mated  with  long-haired 
animals,  produce  short-haired  and  long-haired  young  in  equal  numbers 
if  segregation  occurs  in  every  case  where  it  is  expected.  In  the  mat- 
ings  in  question  there  have  been  produced  10  short-haired  young  and  16 
long-haired  ones — further  evidence  that  segregation  is  less  frequent  than 
expected.  It  is  true  that  these  numbers  are  yet  small,  but  their  uniform 
deviation  in  one  direction  from  the  expected  result  indicates  that  they  are 
significant.  If  so,  we  must  recognize  in  this  pair  of  characters  full 
Mendelian  dominance,  attended,  however,  with  only  partial  Mendelian 
segregation. 

CORRELATION  AMONG  COAT-CHARACTERS. 

In  the  preceding  pages  we  have  discussed  separately  the  heredity  of 
three  different  pairs  of  alternative  coat-characters  which  we  have  found 
to  conform  more  or  less  closely  with  Mendel's  law  of  heredity.  It 
remains  to  inquire  whether  there  is  any  correlation  between  one  of 
these  pairs  of  characters  and  another,  /.  e.,  whether  rough  coat  is 
more  often  associated  with  white  or  with  pigmented  coat,  with  long 
or  with  short  coat,  etc.  An  inquiry  of  this  sort  may  be  based  upon  ex- 
periments made  with  the  albino  male  2002  (PI.  i,fig.  i),  which  possessed 
the  recessive  members  of  two  of  the  pairs  of  characters  (viz,  albinism 
and  long-coat),  but  the  dominant  member  of  the  third  pair  (viz,  rough 
coat).  It  goes  without  saying  that  he  was  pure  as  regards  albinism 


68  COAT   CHARACTERS    IN   GUINEA-PIGS   AND   RABBITS. 

and  long-coat,  for  all  long-haired  albinos  are  pure  in  these  characters, 
and  as  the  result  of  experiment  it  may  be  stated  that  he  was  likewise 
pure  as  regards  the  third  or  dominant  character,  rough  coat.  He  was 
mated  with  nine  different  pure  pigmented,  short-haired,  and  smooth 
females,  producing  29  young,  all  pigmented,  short-haired,  and  rough 
(see  PI.  2,  figs.  3  and  4),  but,  presumably,  all  containing  the  three  cor- 
responding recessive  characters — albinism,  long  coat,  and  smooth  coat. 
He  was  likewise  mated  with  three  other  pigmented  short-haired, 
smooth  females,  which  differed  from  those  previously  mentioned  only 
in  this,  that  they  contained  recessive  albinism.  They  produced  by 
this  mating  15  young,  of  which  all,  of  course,  were  short-haired  and 
rough,  but  9  were  albinos  and  6  pigmented.  The  latter  should  be 
similar  in  nature  to  the  29  young  of  the  matings  previously  described, 
making  in  all,  from  matings  of  cT  2002,  35  young  bearing  the  three 
dominant  characters,  but  supposed  to  contain  the  corresponding  reces- 
sives,  /.  e.,  to  be  hybrid  in  all  three  pairs  of  characters.  A  number  of 
these  young  which  were  tested  by  suitable  matings  proved  to  be  of  the 
character  expected.  They  have  produced  by  different  matings  all  the 
eight  possible  visibly  different  combinations  of  characters,  viz  : 

(i.)  Pigmented  rough  short,  P.  R.  Sh.  (compare  PI.  2,  fig.  4). 
(2.)  Pigmented  rough  long,  P.  JR.  L.  (compare  PI.  5,  fig.  9). 
(3.)  Pigmented  smooth  short,  P.  Sm.  Sh.  (compare  PI.  3,  fig.  6). 
(4.)  Pigmented  smooth  long,  P.  Sm.  L.  (compare  PI.  5,  fig.  jo). 
(5.)  Albino  rough  short,  A.  R.  Sk.  (compare  PI.  2,  fig.  3). 
(6.)  Albino  rough  long,  A.  JR.  L.  (compare  PI.  i,  fig.  i). 
(7.)  Albino  smooth  short,  A.  Sm.  Sh.  (compare  PI.  4,  fig.  7). 
(8.)  Albino  smooth  long,  A.  Sm.  L.  (compare  PI.  4,  fig.  8). 

This  result  shows  clearly  that  there  is  no  necessary  correlation  be- 
tween either  character  of  one  pair  and  either  character  of  another  pair. 
On  the  hypothesis  that  each  pair  of  characters  is,  in  its  transmission, 
•wholly  independent  of  the  others,  i.  £.,  that  no  correlation  whatever 
exists  among  the  pairs,  we  should  expect  triple  hybrids,  like  the  35 
young  of  c?  2002  already  described,  to  produce,  when  mated  inter  se, 
young  visibly  of  the  eight  different  sorts  just  enumerated  in  the  following 
proportions :  27  P.  R.  Sh.,  9  P.  R.  L.,  9  P.  Sm.  -SV&.,  3  P.  Sm.  L., 
9  A.  R.  Sh.,  3  A.  R.  L.,  3  A.  Sm.  Sh.,  i  A.  Sm.  L.  It  will  be 
noticed  that  at  least  64  young  must  be  reared  to  an  age  at  which  all 
three  coat-characters  can  be  determined  before  we  may  expect  all  these 
classes  to  be  represented  among  the  offspring.  As  yet  only  8  young 
have  been  reared  to  such  an  age,  so  that  the  results  are  scarcely  signifi- 
cant quantitatively,  yet  they  indicate  that  the  classes  which  are  expected 
to  be  largest  will  really  be  so,  for  the  eight  young  are  distributed  thus : 
4  P.  R.  Sh.,  3  P.  R.  L.,  i  P.  Sm.  Sh. 

Certain  of  the  triple-hybrid  offspring  of  c?  2002  were  mated  in  ways 


COAT    CHARACTERS    IN    GUINEA-PIGS   AND    RABBITS.  69 

other  than  inter  se,  which  should  give  some  indication  of  whether  any 
correlations  exist  among  the  three  pairs  of  coat-characters.  Thus 
triple  hybrids  were  mated  with  several  pure  pigmented,  smooth,  and 
short-haired  individuals,  P.  Sm.  Sh.,  as  follows: 


Parents. 

Young. 

P.  (A.)  R  (Sm.) 
SA.  (L). 

P.  Sm.  Sh. 

Rough. 

Smooth. 

cT  2036....  
c?  2036  ... 

9  972  
9  973  

2 

3 
3 

2 

3 

i 

I 

2 
I 

5 

CT  2O?7  

9  906  

c?2037  

9  9  907  and  922  

9QIC 

O     Q-I-I 

c?  2°37  

J  933"  

9  9  2033-5  
Total 

c?  2061  

4 

»5 

»3 

All  the  young  were,  as  expected,  pigmented  and  short-haired.  It  is 
expected,  further,  that  half  will  be  rough,  half  smooth,  and  this  result 
is  approximated  in  the  observed  15  rough  to  13  smooth.  The  young, 
though  visibly  of  only  two  sorts,  should  be — on  the  hypothesis  that  no 
correlations  exist  among  the  pairs  of  coat-characters— of  eight  different 
sorts,  all  equally  numerous.  For  the  gametes  of  the  triple  hybrids 
should  be  as  follows :  P.  R.  Sh.  +  P.  R.  L.  +  P.  Sm.  St.  +  P.  Sm. 
L.  +  A.  R.  Sh.  +  A.  R.  L.  +  A.  Sm.  Sh.  +  A.  Sm.  L.  But  the 
gametes  of  the  pure  mates  used  should  all  be  P.  Sm.  Sh.,  and  the 
zygotes  formed  (i.  e.,  the  characters  present  in  the  young)  should  be 
with  equal  frequency  of  these  eight  sorts,  parentheses  indicating  reces- 
sives  not  visible  : 


5.  P.(A.)R.  (Sm.)  SA. 

6.  P.  (A.)  R.  (Sm.)  SA.  (L.) 

7.  P.  (A.)  Sm.  SA. 

8.  P.  04.)  Sm.  SA.  (L.) 


1.  P.  R.  (Sm.)  SA. 

2.  P.  R.  (Sm.)  SA.  (L.) 

3.  P.  Sm.  SA. 

4.  P.  Sm.  SA.  (L.) 

The  tests  to  determine  what  recessives  each  of  the  young  possesses 
are  not  yet  complete,  but  thus  far  show  the  following  distribution  : 

Class  i.   i  (or  2)  individuals.  Class  5.  i  individual. 

Class  2.   i  (or  2)  individuals.  Class  6.  2  (or  3)  individuals. 

Class  3.   i  individual.  Class  7.  None. 

Class  4.  None.  Class  8.  4  individuals. 

Considering  that  only  ten  individuals  have  as  yet  been  fully  tested, 
their  distribution  among  the  classes  is  sufficiently  wide  to  indicate  the 
probable  absence  of  correlation  among  the  three  pairs  of  coat-characters. 
The  full  details  of  the  several  tests  on  which  this  classification  of  indi- 
viduals is  based  will  be  given  in  a  subsequent  report  when  a  larger 
number  of  tests  has  been  completed. 


COAT    CHARACTERS    IN    GUINEA-PIGS   AND    RABBITS. 


EXPERIMENTS  WITH  RABBITS. 

Certain  experiments  with  rabbits,  while  less  extensive  than  those 
made  with  guinea-pigs,  serve  to  confirm  and  extend  some  of  the  con- 
clusions already  reached. 

CROSS    BETWEEN    TWO    DIFFERENT    TYPES    OF   ALBINOS. 

Particularly  instructive  are  the  experiments  with  two  different  types 
of  albinos,  the  pure  or  wholly  unpigmented  type,  and  the  Himalayan 
or  peripherally  pigmented  type. 

A  pair  of  Himalayans  purchased  of  a  dealer  produced  in  two  succes- 
sive litters  only  good  Himalayan  young,  12  in  number.  Presumably, 
therefore,  they  were  pure. 

A  pure  white  female  rabbit  born  of  pigmented  parents,  but  herself 
wholly  unpigmented,  was  likewise  found  to  breed  true  when  mated  to 
animals  like  herself.  Crosses  were  now  made  between  the  two  breeds, 
as  follows : 


Parents. 

Young. 

Pure  white. 

Himalayan. 

Dark 

Himalayan. 

Inter- 
mediate. 

Mosaic. 

9  i  
9  i  

Total 

C?6  
<?7  

2 

3 

2 

i 
3 

3 

5 

4 

All  the  young  had  pigmented  extremities  ;  some  were  nearly  or  quite 
as  heavily  pigmented  as  those  of  the  Himalayan  parent,  but  others  had 
pigmentation  less  heavy  than  that  of  the  Himalayan  parent ;  these  we 
may  call  intermediate.  Still  others  bore  pigment  on  part  only  of  the 
areas  which  are  pigmented  in  a  pure  Himalayan  ;  thus  the  foot  might 
be  pigmented,  but  its  toes  pure  white,  or  the  center  of  the  nose  white, 
with  a  sooty  band  lying  above  and  to  either  side  of  it.  Individuals  such 
as  this  we  may  call  mosaics.  Dominance  of  the  peripheral  pigmentation 
was,  accordingly,  very  imperfectly  realized  in  the  hybrid  offspring. 
Nevertheless,  segregation  of  the  two  types  of  albino  character  involved 
in  this  cross  takes  place  with  great  regularity  when  the  hybrids  form 
gametes,  and  this  is  true  alike  of  all  three  sorts  of  young,  the  dark 
Himalayan,  the  intermediate,  and  the  mosaic,  as  the  following  matings 
show. 


COAT    CHARACTERS    IN    GUINEA-PIGS    AND    RABBITS. 


Parents. 

Young. 

Hybrid. 

Pure  white. 

Dark 
Hima- 
layan. 

Inter- 
mediate 
mosaic. 

Inter- 
mediate. 

Pure 
white. 

Dark  HimaPn  9  24. 

<?  56  

0    i 

2 

2 
2 

2 

3 

2 

Intermediate  c?  19  .. 
Total 

9    SI  

I 

i 

3 

4 

7 

8 

The  observed  result  approximates  equality  of  the  pigmented  and 
unpigmented  classes  of  albinos,  as  expected  on  the  hypothesis  that 
segregation  occurs  in  all  cases.  The  one  good  Himalayan  produced  by 
the  intermediate  cf  19  is  noteworthy  as  showing  that  the  full  Himalayan 
character  was  present  in  the  hybrid  and  capable  of  segregation,  though 
seen  in  a  partially  dominated  condition  in  the  hybrid  himself.  Similar 
cases  occur  in  the  matings  enumerated  below.  Apparently  cases  of 
this  sort  are  like  those  of  the  imperfect  rough  guinea-pigs  produced  by 
certain  smooth  animals  in  crosses  with  rough  ones,  which  nevertheless 
were  capable  of  transmitting  the  rough  character  in  its  full  intensity. 

Further  evidence  of  segregation  of  the  Himalayan  and  pure  white 
types  of  albino  character  in  the  gametes  of  the  hybrids  is  afforded  by 
mating  these  inter  se,  as  the  following  experiments  show. 


Young. 

Himalayan  type. 

p 

Hybrid. 

Hybrid. 

D. 

D.  M. 

I.  M. 

/. 

I.  C?  19  

I.    9    21  

i 

i 

i 

4 

... 

I.  c?  19  

D.   9  23  

i 

... 

I.  d1  19  

D.  9  24  

2 

2 

... 

3 

D.  M.  c?  20  

I.  9  21  

I 

i 

2 

... 

3 

D.  M.  cT  20  

I.    9    22  

2 

3 

3 

i 

D.  M.  cT  20  

D.   9  23  

3 

i 

9 

3 

8 

8 

7 

28 

D.  M.  c?  20  

I.  9  21  

6 

i 

I.  M.  c?45  

D.  M.  9  108.... 

3 

3 

I.  M.  c?45  

D.  9  109  

5 

i 

Totals  observer!    

42 

12 

Totals  expec 

ted  

4°* 

13* 

Explanation.— D.  =  fully  pigmenttd  or  dark  Himilayan ;  D.  M.  =  dark  mosaic ;  /.  M.  =  inter- 
mediate mosaic ;  /.  =  intermediate ;  P.  =  pure  white. 


COAT   CHARACTERS    IN    GUINEA-PIGS    AND    RABBITS. 


The  observed  numbers  of  Himalayan  and  pure  white  young,  it  will 
be  noticed,  approximate  fairly  well  the  numbers  expected  on  the  hy- 
pothesis of  complete  segregation. 

The  possibility  of  transmuting  the  Himalayan  type  into  the  pure 
white  type  by  cross-breeding  is  suggested  by  an  interesting  experiment 
performed  by  Raspail  (  :  02).  He  set  at  liberty  in  a  park  frequented 
by  wild  gray  rabbits,  a  Russian  female  rabbit,  which  variety  has 
the  Himalayan  type  of  peripheral  pigmentation.  The  female  was 
presumably  fertilized  by  wild  males,  certainly  by  pure  pigmented 
animals,  as  the  outcome  indicates.  In  three  successive  litters  she  pro- 
duced only  self  colored  gray  or  black  young,  in  numbers  approxi- 
mately equal,  as  follows  :— 


Gray. 

Black. 

Litter  i     ..    . 

7 

6 

Litter  2   

I 

Litter  3          .     ... 

I 

Total   

18 

16 

Certain  of  the  gray  hybrids  bred  inter  se  produced  5  gray  young,  3 
white  ones  [apparently  Himalayan],  and  I  pure  white.  Two  of  the 
[Himalayan]  whites,  when  mated  inter  se  produced  a  litter  of  4  [Hima- 
layan] white  young.  Two  of  these  in  turn  interbred  produced  5  pure 
white  offspring. 

This  experiment  I  attempted  to  repeat,  substituting  for  the  wild 
pigmented  parent  a  pure  reddish  gray  pigmented  animal  of  the  breed 
known  as  the  Belgian  hare.  A  female  Belgian  hare  was  mated  with 
Himalayan  cf  6,  the  original  male  employed  in  the  experiments  already 
described.  Three  young  were  reared,  a  male  and  two  females,  of  a 
gray  color  somewhat  darker  than  that  of  the  mother,  since  it  contained 
more  black  pigment.  The  hybrids  bred  inter  se  have  produced  young 
as  follows : — 


Young. 

Parents. 

Gray. 

Black. 

Hima- 
layan. 

<J  48  x  9  49 

2 

(A?)* 

c?48  x  $  50  
cT  48  x  9  5°  

5 
5 

I 

3 

I 

2 

Total  

2 

D 

6 

'  Gray  or  black,  died  early. 


COAT    CHARACTERS    IN    GUINEA-PIGS    AND    RABBITS.  73 

It  is  expected  that  one-fourth  of  the  young  will  be  albinos,  and  this 
proportion  is  approximated.  But  all  six  of  the  albinos  thus  far  ob- 
tained have  pigmented  extremities,  as  did  their  Himalayan  grand- 
father. No  pure  whites  have  been  produced.  In  this  respect  my 
results  differ  from  those  of  Raspail.  It  is  true  that  the  intensity  of 
pigmentation  of  these  extracted  Himalayans  varies  considerably,  as 
does  that  of  the  pigmented  young.  There  are  dark  and  light  Hima- 
layans, just  as  there  are  dark  and  light  grays,  among  the  offspring. 
Cross-breeding  has  in  this  case,  as  in  others,  been  the  cause  of  variation 
within  the  types  of  the  parents,  but  I  have  no  evidence  as  yet  that  it 
can  completely  remove  the  pigmentation  from  the  Himalayan  albino 
type,  thus  converting  it  into  a  pure  albino.  Nevertheless  further  ex- 
periments may  lead  to  this  result,  yet  I  hardly  expect  it  in  view  of  the 
distinctness  shown  by  the  Himalayan  and  the  pure  albino  types  in  the 
experiments  already  described.  I  suspect,  rather,  that  the  Russian 
female,  with  which  Raspail  began  his  experiments,  was  in  reality  a 
hybrid,  like  those  which  I  have  described  on  page  70,  in  which  pure 
albinism  was  recessive.  Raspail  says  concerning  her,  page  172  : 

La  femelle  de  Lapin  russe  qui  m'a  servi  pour  mes  experiences,  n'e*tait  pas  de 
race  pure  :  le  museau,  I'extre'mit^  des  pattes,  les  oreilles  et  le  dessus  de  la  queue 
e*taient  d'un  noir  moins  franc  et  moins  veloute';  sa  taille  etait  notablement  plus 
forte  et  ses  yeux  rouges  indiquaient  qu'elle  tournait  a  Palbinisme. 

This  explicit  statement  and  description  certainly  favors  the  idea  that 
she  was  a  cross-bred  with  a  pure  albino  race,  which,  if  true,  would 
fully  explain  the  occurrence  of  pure  albinos  in  her  offspring  of  genera- 
tion F2,  without  necessitating  the  conclusion  that  the  peripherally 
pigmented  type  of  albino  had  been  transmuted  into  the  unpigmented 
type  by  cross-breeding. 

HEREDITY    OF   LONG   OR    "ANGORA"    COAT. 

This  character  is  in  rabbits,  as  in  guinea-pigs,  a  recessive  Mendelian 
character.  Dominance  and  segregation  both  appear  to  be  complete  in 
crosses  between  normal  (or  short-haired)  and  angora  (or  long-haired) 
rabbits.  I  have  observed  in  this  case  neither  formation  of  intermediates, 
i.  <?.,  of  inferior  long-haired  specimens,  nor  deviation  from  the  expected 
proportions  of  long-haired  and  short-haired  individuals,  of  which  con- 
ditions there  were  some  indications  in  guinea-pigs.  But  in  one  or  two 
cases  I  have  thought  that  1  could  recognize  in  hybrids  a  greater  soft- 
ness of  the  coat,  just  as  in  guinea-pigs  which  are  cross-breds  between 
long-haired  and  short-haired  races. 

The  numbers  of  young  thus  far  reared  are  small,  and  not  much 
weight  is  to  be  attached  to  them,  so  far  as  quantitative  results  are  con- 
cerned. 


I 


74  COAT    CHARACTERS    IN    GUIVKA-PIGS    AND    RABBITS. 

In  detail  the  matings  made  are  as  follows : 


Parents. 

Young. 

Long. 

Short. 

Short. 

Long. 

c?N  . 

$  9  17,  18,  and  28.. 
6  Lop  

10 
8 

::: 

tf  4C  

Total 

18* 

... 

Short  (LJ 

Short  (L.) 

Short. 

Long. 

9  i        

Brother  

4 

i 

2 
2 

9  i                 .... 

C?  20  (son)         

921  

Total   

(?  20  

15+ 

5 

Long. 

Short  (L.) 

Short. 

Long. 

r?  4<C 

9  108 

2 

4 

4 

2 

O    4o  
r?  -jc  

9  IOQ... 

Total 

6J 

6 

•  Expected,  all  short.  t  Expected,  3  short :  i  long.  t  Expected,  i  short :  i  long. 

EXPLANATION  — L.  =  long-haired  or  angora.     Parentheses  indicate  recessive  characters  not  visible. 

HEREDITY    OF   LOP-EARS. 

Some  experiments  are  likewise  in  progress  with  the  inheritance  of 
the  large  or  lop-eared  character  in  rabbits,  but  these  are  hardly  far 
enough  advanced  to  make  their  outcome  certain.  The  young  produced 
by  a  cross  between  two  breeds  having  ears  of  different  relative  size 
themselves  have  ears  of  an  intermediate  size.  In  other  words,  there  is 
no  evidence  of  dominance.  A  second  generation  of  young  has  been 
obtained,  but  is  not  yet  fully  grown  ;  apparently  they  too  will  have  ears 
of  an  intermediate  character.  If  so,  we  may  conclude  that  segregation 
as  well  as  dominance  is  wanting  in  this  case,  which  would  seem  to  be 
one  of  blended  or  non-Mendelian  inheritance,  similar  to  that  of  the 
willow-hybrids  studied  by  Wichura  and  that  of  the  Hieracium  hybrids 
of  Mendel  ('70). 


\ 


COAT    CHARACTERS    IN    GUINEA-PIGS    AND    RABBITS.  75 


SUMMARY. 

(1)  There  occur  among  domesticated  guinea-pigs  three  pairs  of  alter- 
native coat-characters  which  conform  in  their  inheritance  to  Mendel's 
law  of  heredity.    These  are  (i)  albinism,  which  is  recessive  with  respect 
to  pigmented  coat ;  (2)  smooth  coat,  which  is  recessive  with  respect  to 
rough  coat ;  and  (3)  long  coat,  which  is  recessive  with  respect  to  short 
coat.     Two  of  the  recessive  characters,  viz,  albinism  and  long  coat,  are   \ 
doubtless  characters  of  comparatively  recent  origin,  which  have  made     1 
their  appearance  since  the  guinea-pig  was  domesticated.     The  third 
recessive  character,  smooth  coat,  is  undoubtedly  ancestral,  and  curiously 
enough  is  regularly  dominated  by  rough  coat,  a  character  probably  of 
recent  origin,  for  a  cavy  bearing  rosettes  like  those  of  the  "  Abyssinian  " 
guinea-pig  is  unknown  in  a  wild  state.     This  indicates  that  ancestral 
characters  are  not  necessarily  dominant  over  new  characters  in  heredity. 
The  three  pairs  of  characters  are  probably  wholly  uncorrelated. 

(2)  In  rabbits  occur  two  of  the  three  pairs  of  alternative  coat-charac» 
ters  which  are  found  in  guinea-pigs.     Here,  too,  albinism  and  long  or 
"  angora"  coat  are  recessive  characters.     A  resetted  or  rough  coat  is 
unknown  in  rabbits. 

(3)  A  sharp  distinction  must  be  made  between  characters  which 
are  recessive  and  those  which  are  latent.     Recessive  characters  dis- 
appear from   an  individual  in  which  they   are   associated    with   the 
corresponding  dominant  character,  yet  they  reappear  distinct  in  half 
the  gametes  formed  by  that  individual ;  latent  characters  are  characters 
normally  dominant,  which    have   disappeared    in    recessive   gametes 
beyond  hope  of  recall,  except  under  conditions  of  cross-breeding  which 
are  in  most  cases  not  entirely  clear.     Albino  gametes  transmit  in  a 
latent  condition  both  specific  pigment  characters  and  specific  color- 
patterns.     These  latent  characters  can  be  brought  into  activity  only  by 

cross-breeding  with  a  pigmental  animal.      The  rough  coat-character  \ 
I  may  likewise  become  almost  completely,  if  not  quite  completely,  latent  | 
y  in  smooth  animals.     These  facts  indicate  a  possible  explanation  of  the 
observed  slight  excess  of  recessives  over  the  Mendelian  expectation  in 
cases  involving  one  or  the  other  of  these  two  pairs  of  characters.     In 
the  case  of  the  long  -vs.  short  pair  of  characters,  an  excess  of  recessives    . 
and  the  occurrence  simultaneously  of  intermediates  in  generation  F,, 
but  not  in  Fn  are  more  probably  due  to  imperfect  segregation  than  to 
latency  of  the  dominant  character.     It  is  possible,  however,  that/ar/tf£ 
latency  and  imperfect  segregation  are  related,  if  not  identical  phenomena. 


76  COAT    CHARACTERS    IN    GUINEA-PIGS    AND    RABBITS. 

/     (4)  Some  recessive  individuals  are  prepotent,  for  their   gametes, 

'    when  united  with  those  of  ordinary  dominants,  produce  young  of  an 

intermediate  character.    These  intermediates,  however,  have  the  power 

/  to  transmit  the  full  dominant  character  in  matings  with  recessive  incli- 

/  viduals.     There  is  reason  to  believe,  accordingly,  that  the  dominant 

V  character  is  in  such  cases,  not  partially  latent,  but  partially  dominated. 

If  so,   we  have  in  cases  if  this  sort  something  remotely  resembling 

the  alternative  dominance  seen  in  certain  of  the  crosses  among  silk 

moths  made  by  Coutagne  (  :  02). 

/     (5)  The  lop-eared  condition  in  rabbits  is  probably  a  non-Mendelian 
/character  in  its  relation  to  normal  ear;  for  the  children  and  grand- 
ychildren  produced   by  crosses   are  apparently  alike    intermediate  in 
character. 

(6)  A  cross  between  two  different  types  of  albino  rabbits,  Himalayan  \ 
and  pure  white,  shows  imperfect  dominance  of  the  Himalayan  character^/ 
in  the  offspring,  but  complete  segregation  among  their  gametes. 

(7)  Cross-breeding    between    dominant  and    recessive    individual* 
may  lead  to  the  production  of  new  sorts  of  individuals  in  a  variety  of 
ways,  e.  £.,  (i)  by  producing  new  combinations  among  different  pairs 
of  alternative  characters,  as  among  the  children  of  triple-hybrid  guinea- 
pigs  ;   (2)  probably  by  causing  a  complex  character,  like  the  agouti  coat 
of  guinea-pigs,  to  break  up  into  its  elements — black,  chocolate,  and  yel- 
low— one  or  more  of  the  elementary  pigment  characters  either  becoming 
latent  or  passing  bodily  out  of  the  gamete  ;   (3)   by  the  coming  into 
activity  of  elements  of  the  dominant  character  which  were  latent  in 
recessive  gametes,  as  black  latent  in  albino  guinea-pigs  or  in  Himalayan 
rabbits  (see  next  report) ;  (4)  by  inducing  variability  in  the  intensity  of 
characters,  quite  aside  from  resolution  and  recombination  of  characters, 
as  when  red  cross-bred  with  black  produces  a  very  light  shade  of  red, 
e.  g.,  yellow  or  cream. 


COAT    CHARACTERS    IN    GUINEA-PIGS    AND    RABBITS.  77 


BIBLIOGRAPHY. 

Allen,  G.  M. 

:  04.    The    heredity  of  coat  color  in   mice.     Proc.  Amer.  Acad.  Arts  and 

Sci.,  vol.  40,  no.  2,  pp.  61-163,  7  figs. 
Bateson,  W. 

:o2.     Mendel's  principles  of  heredity,  a   defence.     With    a   translation  of 
Mendel's  original  papers  on  hybridisation,     xiv  -+•  212  pp.     Cam- 
bridge.    [England.     Contains  bibliography  and  portrait  of  Mendel.] 
Bateson,  W. 

:  03.     The  present  state  of  knowledge  of  colour-heredity  in  mice  and  rats. 

Proc.  Zool.  Soc.  London,  1903,  vol.  2,  pp.  71-99. 
Castle,  W.  E. 

103.     Mendel's  law  of  heredity.     Proc.  Amer.  Acad.  Arts  and  Sci.,  vol.  38, 

no.  18,  pp.  535-548. 
Castle,  W.  E. 

103^.     Mendel's    law   of  heredity.     Science,   n.    s.,   vol.    18.  No.  456,   pp. 
396-406,  September  25,   1903.     [A  reprint  of  the  foregoing,  with 
some  additions  and  corrections.] 
Castle,  W.  E. 

:o3b.     The  laws  of  heredity  of    Gallon  and  Mendel,  and  some  laws  gov- 
erning race  improvement  by  selection.     Proc.  Amer.  Acad.  Arts 
and  Sci.,  vol.  39,  no.  8,  pp.  223-242. 
Castle,  W.  E. 

1030.     The  heredity  of  "  Angora"  coat  in  mammals.      Science,  n.  s.,  vol. 

1 8,  no.  467,  pp.  760-761,  December  n,  1903. 
Castle,  W.  E.,  and  Allen,  G.  M. 

103.     The  heredity  of  albinism.     Proc.  Amer.  Acad.  Arts  and  Sci.,  vol.  38, 

pp.  603-622. 
Coutagne,  G. 

:  02.     Recherches  exp6rimentales  sur  1'he're'dite'  chez  les  vers  a  soie.     Bull. 

Sci.  France  et  Belg. ,  torn.  37,  pp.  1-194,  P'S-  I-9- 
Cuenot,  L. 

-.03.     L'he're'dite  de  la  pigmentation  chez   les   souris.     (2m*  note.)    Arch. 
Zool.  Expdr.  et  Ge"n.,  se"r.  4,  torn,  i,  Notes  et  Revue,  pp.  xxxiii-xli. 
Cuenot,  L. 

-.04.     L'he're'dite'  de  la  pigmentation  chez  les  souris.     (3me  note.)      Arch. 

Zool.  Expe"r.  et  Ge"n.,  ser.  4,  torn.  2,  Notes  et  Revue,  pp.  xlv  -Ivi. 
Cumberland,  C. 

[Date?]  The  guinea-pig,  or  domestic  cavy,  for  food,  fur,  and  fancy.     100  pp., 

illus.,  London.     L.  Upcott  Gill. 
Darbishire,  A.  D. 

103.    Third  report  on  hybrids  between  waltzing  mice  and  albino  races. 

Biometrika,  vol.  2,  pt.  3,  pp.  282-285. 
Darbishire,  A.  D. 

:  04.    On  the  result  of  crossing  Japanese  waltzing  with  albino  mice.     Biome- 
trika, vol.  3,  pt.  i,  pp.  1-51,  8  figs. 

'97'.     The  average  contribution  of  each  several  ancestor  to  the  total  heritage 
of  the  offspring.     Proc.  Roy.  Soc.,  London,  vol.  61,  pp.  401-413. 

Guaita,  G.  von. 

'98.    Versuche  mit  Kreuzungen  von  verschiedenen  Rassen  des  Hausmaus. 
Ber.  naturf.  Gesellsch.  zu  Freiburg,  Bd.  10,  pp.  3I7-332- 


78  COAT    CHARACTERS    IN    GUINEA-PIGS    AND    RABBITS. 

Guaita,  G.  von. 

:oo.    Zweite  Mittheilungiiber  Versuche  mit  Kreuzungen  von  verschiedenen 
Rassen  des  Hausmaus.     Ber.  naturf.  Gesellsch.  zu  Freiburg,  Bd.  n, 
pp.  131-138,  3  Taf. 
Haacke,  W. 

'95.    Ueber  Wesen,Ursachen  und  Vererbung  von  Albinismus  und  Scheckung, 
und  iiber  deren  Bedeutung  fur  vererbungstheoretische  und  entwick- 
lungs-mechanische  Fragen.     Biol.  Centralbl.,  Bd.  15,  pp.  44-78. 
Loeb,  L. 

'97.     Ueber  Transplantation  von  weisser  Haul  auf  einem  Defect  in  schwarzer 
Haul  und  umgekehrt  am  Ohr  des  Meerschweinschens.    Arch.  Entw.- 
Mech.,  Bd  6,  pp.  1-44,  3  Taf.,  2  Fig. 
Mendel.  G. 

'66.     Versuche  iiber  Pflanzenhybriden.      Verh.  Naturf.  Vereins  in  Briinn, 

Bd.  4,  Abh.,  pp.  3-47.     [Translation  in  Bateson,  :o2.] 
Mendel,  G. 

'70.     Ueber  einige  aus   kiinstlicher  Befruchtung    gewonnenen  Hieracium- 
Kastarde.     Verh.  Naturf.  Vereins  in  Briinn,  Bd.  8,  Abh.,  pp.  26-31. 
[Translation  in  Bateson.  :o2.] 
Pearson,  K. 

104.     A  Mendelian's  view  of  the  law  of  ancestral  inheritance.     Biometrika, 

vol.  3,  pt.  i,  pp.  109-112. 
Raspail.  X. 

:  02.     Note  surune  race  de  lapins  albinos  issue  du  croisement  d'une  femelle 
tie  lapin  russe  et  d'un  male  garenne  (Lepus  cuniculus).     Bull.  Soc. 
Nat.  d'Acclimatation  de  France,  49me  ann6e,  pp.  170-175. 
Shaw,  T. 

103.     The  study  of  breeds  in  America.     Cattle,  sheep,  and  swine,     xvi  -)• 
371  pp.,  illus.     Orange  Judd  Co.,  N.  Y. 


PLATE  1. 


FIG.  1.— A  LONG-HAIRED,  ROUGH,  ALBINO  GUINEA-PIG,  C?  2002. 

Pure  (*'.  e.,  homozygous)  as  regards  all  three  coat-characters,  two  of  which  are  recessive 
in  nature,  one  dominant.  Fanciers'  name  for  all  animals  of  this  appearance,  whether 
homozygous  or  heterozygous  in  character,  White  Peruvian. 


FIG.  2.— A  SHORT-HAIRED,  SMOOTH,  RED  GUINEA-PIG,  9  1355. 

Pure  in  respect  to  two  of  its  coat-characters,  viz,  smooth  coat  and  pigtnented  coat,  but 
heterozygous  as  regards  the  third,  since  it  contains  recessive  long  coat,  though  its  own 
coat  is  no  longer  than  that  of  most  pure  short-haired  animals.  Toes  of  right  fore  foot  whUe. 
Fanciers'  name  for  animals  of  this  appearance,  whether  or  not  homozygous,  Red  Enghsh. 


PLME  2. 


FIG.  3.— A  SHORT-HAIRED,  ROUGH,  ALBINO  GUINEA-PIG,  C?  1095. 
Son  of  c?  2002  (fig.  1,  pi.  1)  and  of  Red  English  $  3,  which  contained  recessive 
albinism,  but  was  otherwise  homozygous  (compare  fig.  2,  pi.  1).  This  animal  is  a  double 
heterozygote,  containing  recessive  the  two  characters,  long  coat  and  smooth  coat.  As 
regards  albinism,  it  is,  of  course,  pure.  Fanciers'  name  for  all  animals  of  this  appearance, 
White  Abyssinian. 


' 


FIG.  4.— A  SHORT-HAIRED,  ROUGH,  BLACK-RED  PIGMENTED  GUINEA-PIG,  O    2037. 

Son  of  cf  2002  (fig.  1,  pi.  1)  and  of  pure  Red  English  ?  755  (compare  fig.  2,  pi.  1). 
A  triple  heterozygote  containing  recessive  the  three  characters,  long  coat,  smooth  coat, 
and  albino  coat.  The^black  pigment  seen  in  this  animal's  coat  was  inherited,  not  from 
the  red  pigmented  mother,  but  from  the  albino  father.  Unfortunately  black  areas  are 
scarcely  distinguishable  from  red  ones  in  the  figure.  Fanciers'  name  for  all  animals  of 
this  appearance,  Tortoise-shell  Abyssinian. 


PLATE  3. 


FIG.  5.— A  LONG-HAIRED,  SMOOTH,  ALBINO  GUINEA-PIG,  $  2060. 

From  inspection  alone  of  this  animal,  one  may  know  that  it  is  pure  as  regards  coat- 
characters,  since  it  manifests  the  three  which  are  by  nature  recessive.  Fanciers  tiutnt  , 
White  Angora. 


FIG.  6.— A  SHORT-HAIRED,  SMOOTH,  RED-BLACK  PIGMENTED  GUINEA-PIG. 

The  parents  were  both  triple  heterozygotes  (compare  fig.  4,  pi.  2).  This  animal  is.  of 
course,  pure  as  regards  smooth  coat,  but  whether  it  contains  the  two  recessive  characters 
which  it  does  not  manifest,  can  be  determined  only  by  breeding  tests.  In  this  figure,  as 
in  fig.  4,  black  areas  unfortunately  are  indistinguishable  from  red  ones.  Fanciers'  name 
for  all  animals  of  this  appearance,  whether  pure  or  heterozygous,  Tortoise-shell  English. 


PLATE  4. 


FIG.  7.— A  SHORT-HAIRED,  SMOOTH,  ALBINO  GUINEA-PIG,  *   1499. 

Daughter  of  two  albino  parents,  viz,  9  991,  a  double  heterozygote  like  •$  1095  (fig.  4, 
pL  2),  and  $  635,  a  pure  short-haired,  smooth  animal.  We  know  without  experimental 
test  that  this  animal  is  pure  as  regards  the  two  recessive  characters  which  it  manifests, 
smooth  coat  and  albinism,  but  breeding  tests  are  necessary  to  show  whether  or  not  it  con- 
tains recessive  the  character  long  coat.  This  animal  has  been  found  to  form  prepotent 
smooth  gametes.  Fanciers'  name  for  all  animals  of  this  appearance,  White  English. 


FI3.  8.-A  LONG-HAIRED,  SMOOTH,  ALBINO  GUINEA-PIG,    *    1756. 
Daughter  of  3  2060  (fig.  5.  pi.  3)  and  of  ?  993,  which  was  a  double  heterozygote  like 
C?  1095  (fig.  3.  pi.  2).     This  animal,  like  C?  2060,  being  a  triple  recessive,  is  pure  as  regards 
all  three  coat-characters.     Fanciers'  name.  White  Angora. 


PLATE  6. 


FIG.  11.  — *  PARTIALLY  LONG-HAIRED,  ROUGH,  AND  SPOTTED  GUINEA-PIG,    9  2258. 

Daughter  of  two  triple-heterozygotes  (compare  fig.  4,  pi.  2).  The  long-haired  dial- 
acter  is  imperfectly  developed  in  this  animal,  only  part  of  the  hair  being  long  as  in  the 
Peruvian  grandparent,  cJ*  2002  (fig.  1,  pi.  1). 


FIG.  12.— A  TRIPLE  HETEROZYGOTE,  C?1989a. 

(Compare  fig.  4,  pi.  2.)  Son  of  cf  2002  (fig.  1,  pi.  1)  and  of  black-eyed  white  9 
2005,  which  is  also  a  prepotent  smooth  animal.  The  coat  is  in  part  pigmented;  the 
rough  character  is  imperfectly  developed,  showing  only  one  pair  of  the  rosettes  which  are 
typically  formed  (compare  figs.  3  and  4,  pi.  2). 


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